In this post I thought it would be interesting to take a look at the current situation in the Dothraki Sea.

The Current Status of Daenerys' Plotline in the Dothraki Sea

Readers have theorized a return to the Dothraki Sea or even Vaes Dothrak as far back as ACOK:

Dany's wrist still tingled where Quaithe had touched her. "Where would you have me go?" she asked.
"To go north, you must journey south. To reach the west, you must go east. To go forward you must go back, and to touch the light you must pass beneath the shadow." -ACOK, Daenerys III

And while its quite possible Dany doesn't do everything that GRRM originally intended in that quote, we see the same quote again in ADWD, right before the end of the book:

Off in the distance, a wolf howled. The sound made her feel sad and lonely, but no less hungry. As the moon rose above the grasslands, Dany slipped at last into a restless sleep.
She dreamed. All her cares fell away from her, and all her pains as well, and she seemed to float upward into the sky. She was flying once again, spinning, laughing, dancing, as the stars wheeled around her and whispered secrets in her ear. "To go north, you must journey south. To reach the west, you must go east. To go forward, you must go back. To touch the light you must pass beneath the shadow." -ADWD, Daenerys X

And then Khal Jhaqo does show up:

As the western sky turned the color of a blood bruise, she heard the sound of approaching horses. Dany rose, wiped her hands on her ragged undertunic, and went to stand beside her dragon.
That was how Khal Jhaqo found her, when half a hundred mounted warriors emerged from the drifting smoke. -ADWD, Daenerys X

Khal Jhaqo

He was originally a ko of Drogo's before forming his own khalasar:

"The Dothraki follow only the strong," Ser Jorah said. "I am sorry, my princess. There was no way to hold them. Ko Pono left first, naming himself Khal Pono, and many followed him. Jhaqo was not long to do the same. The rest slipped away night by night, in large bands and small. There are a dozen new khalasars on the Dothraki sea, where once there was only Drogo's." -AGOT, Daenerys IX

There are twenty thousand riders in his khalasar:

The Dothraki exchanged uncertain glances. "Khaleesi," the handmaid Irri explained, as if to a child, "Jhaqo is a khal now, with twenty thousand riders at his back." -AGOT, Daenerys IX

Mago

He was the original man who attempted to rape Eroeh before Dany stepped in. He is now a bloodrider to Jhaqo after being in his ko:

Eroeh?" asked Dany, remembering the frightened child she had saved outside the city of the Lamb Men.
"Mago seized her, who is Khal Jhaqo's bloodrider now," said Jhogo. "He mounted her high and low and gave her to his khal, and Jhaqo gave her to his other bloodriders. They were six. When they were done with her, they cut her throat."
"It was her fate, Khaleesi," said Aggo.
If I look back I am lost. "It was a cruel fate," Dany said, "yet not so cruel as Mago's will be. I promise you that, by the old gods and the new, by the lamb god and the horse god and every god that lives. I swear it by the Mother of Mountains and the Womb of the World. Before I am done with them, Mago and Ko Jhaqo will plead for the mercy they showed Eroeh**.**"-AGOT, Daenerys IX

GRRM confirmed that Mago is going to be a recurring character in TWOW:

So Mago is not dead in the books. And, in fact, he’s going to be a recurring character in Winds of Winter. He’s a particularly nasty bloodrider to one of the other Khals that’s broken away after Drogo dies. -SSM,EW: A Dance with Dragons Interview: 12 July 2011

Search Party

So we know that Dany/Drogo are with the Dothraki. We also know that some search parties are out looking for her (and thank the gods old and new its not buddy cop Jorah and Daario).

Aggo and Rakharo and the rest of the queen's khalasar had been dispatched across the river to search for their lost queen. -ADWD, The Queensguard

and:

Her bloodriders have been dispatched across the Skahazadhan to find Her Grace and return her to her loving lord and loyal subjects. Each has ten picked riders, and each man has three swift horses, so they may travel fast and far. Queen Daenerys shall be found." -ADWD, The Discarded Knight

and:

Missandei nodded. It was hard to tell if she was reassured. "Do you think that they will find her, ser? The grasslands are so vast, and dragons leave no tracks across the sky."
"Aggo and Rakharo are blood of her blood … and who knows the Dothraki sea better than Dothraki?" He squeezed her shoulder. "They will find her if she can be found." If she still lives. There were other khals who prowled the grass, horselords with khalasars whose riders numbered in the tens of thousands. But the girl did not need to hear that. "You love her well, I know. I swear, I shall keep her safe." -ADWD, The Queensguard

When/Where?

I have always assumed it would take place in Vaes Dothrak (something like dragonflame not spilling blood), but Vaes Dothraki is pretty far from Slaver's Bay. So depending on how big of a plotline it is, will seemingly depend on where the climax takes place.

But in the last chapter of ADWD, Vaes Dothrak is mentioned:

Afterward Drogo's great khalasar had shattered. Ko Pono named himself Khal Pono and took many riders with him, and many slaves as well. Ko Jhaqo named himself Khal Jhaqo and rode off with even more. Mago, his bloodrider, raped and murdered Eroeh, a girl Daenerys had once saved from him. Only the birth of her dragons amidst the fire and smoke of Khal Drogo's funeral pyre had spared Dany herself from being dragged back to Vaes Dothrak to live out the remainder of her days amongst the crones of the dosh khaleen. -ADWD, Daenerys X

Vaes Dothrak

The last time Dany was in Vaes Dothraki/at the Mother of the Mountains/Womb of the World, they declared her son Rhaego as "The Stallion that Mounts the World"

"As swift as the wind he rides, and behind him his khalasar covers the earth, men without number, with arakhs shining in their hands like blades of razor grass. Fierce as a storm this prince will be. His enemies will tremble before him, and their wives will weep tears of blood and rend their flesh in grief. The bells in his hair will sing his coming, and the milk men in the stone tents will fear his name." The old woman trembled and looked at Dany almost as if she were afraid. "The prince is riding, and he shall be the stallion who mounts the world." -AGOT, Daenerys V

We also see these crones in a flashback vision during the House of the Undying:

Faster and faster the visions came, one after the other, until it seemed as if the very air had come alive. Shadows whirled and danced inside a tent, boneless and terrible. A little girl ran barefoot toward a big house with a red door. Mirri Maz Duur shrieked in the flames, a dragon bursting from her brow. Behind a silver horse the bloody corpse of a naked man bounced and dragged. A white lion ran through grass taller than a man. Beneath the Mother of Mountains, a line of naked crones crept from a great lake and knelt shivering before her, their grey heads bowed. Ten thousand slaves lifted bloodstained hands as she raced by on her silver, riding like the wind. "Mother!" they cried. "Mother, mother!" They were reaching for her, touching her, tugging at her cloak, the hem of her skirt, her foot, her leg, her breast. They wanted her, needed her, the fire, the life, and Dany gasped and opened her arms to give herself to them . . . -ACOK, Daenerys IV

Wherever it happens, I do expect Dany to hold true to her words:

If I look back I am lost. "It was a cruel fate," Dany said, "yet not so cruel as Mago's will be. I promise you that, by the old gods and the new, by the lamb god and the horse god and every god that lives. I swear it by the Mother of Mountains and the Womb of the World. Before I am done with them, Mago and Ko Jhaqo will plead for the mercy they showed Eroeh."-AGOT, Daenerys IX

I've seen this quote theorized about a bit, but nothing has stood out to me (yet):

"A dragon queen," said Tyrion. "A pleasant omen."
"Her king is missing." Illyrio pointed out the smooth stone plinth on which the second sphinx once stood, now grown over with moss and flowering vines. "The horselords built wooden wheels beneath him and dragged him back to Vaes Dothrak." -ADWD, Tyrion II

Other khals

Its possible Dany could encounter some other khalasars on the Dothraki Sea, but due to where most of them seem located, I think it would be more likely to occur on the way to Volantis.

Zekko/Motho/Pono:

"Zekko visits Qohor every three or four years. The Qohorik give him a sack of gold and he turns east again. As for Motho, his men are near as old as he is, and there are fewer every year. The threat is—"
"—Khal Pono," Haldon finished. "Motho and Zekko flee from him, if the tales are true. The last reports had Pono near the headwaters of the Selhoru with a khalasar of thirty thousand. Griff does not want to risk being caught up in the crossing if Pono should decide to risk the Rhoyne." Haldon glanced at Tyrion. "Does your dwarf ride as well as he pisses?" -ADWD, Tyrion III

and:

"Ko Pono spoke you gently," Ser Jorah Mormont said. "Khal Pono will kill you. He was the first to abandon Drogo. Ten thousand warriors went with him. You have a hundred." -ACOK, Daenerys I

In the AFFC, Appendix (weirdly listed since Dany/Dothraki aren't in that book) these characters are listed as "sometimes allies" of Drogo (although this could be due just to the early Vaes Dothraki scene):

• KHAL MORO, sometime ally of Khal Drogo,

  • RHOGORO, his son and khalakka,

• KHAL JOMMO, sometime ally of Khal Drogo.

Its possible this ruse could be used in the future to take Volantis:

Tyrion understood that quick enough. Alone amongst the major river towns, Selhorys stood upon the eastern bank of the Rhoyne, making it much more vulnerable to the horselords than its sister towns across the river. Even so, it is a small prize. If I were khal, I would feint at Selhorys, let the Volantenes rush to defend it, then swing south and ride hard for Volantis itself. -ADWD, Tyrion VI

As well as this treachery as well:

"You have Dothraki outside your own gates," Haldon said.
"Khal Pono." Qavo waved a pale hand in dismissal. "The horselords come, we give them gifts, the horselords go." He moved his catapult again, closed his hand around Tyrion's alabaster dragon, removed it from the board. -ADWD, Tyrion VI

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All in all I think its likely that the general theory is true: "Dany uses Drogo to conquer the Dothraki", I just think the when/where might be a little ambiguous.

Who knows, maybe Victarion will show up lol:

"The silver queen is gone," the ketch's master told him. "She flew away upon her dragon, beyond the Dothraki sea."
"Where is this Dothraki sea?" he demanded. "I will sail the Iron Fleet across it and find the queen wherever she may be." -ADWD, Victarion I

We can assume GRRM was writing about this plotline in 2012 when he stated:

WINDS OF WINTER. Yes, I'm working on that too. At the moment, I am writing about the Dothraki. More than that, I sayeth not, you know I don't like to talk about this stuff. -SSM, Odds and Ends: 12 May 2012

He also had this to say in a Galaxy Edge Interview in 2014:

“I’m going back to The Winds of Winter and writing the next scene—I’ve got Dany in a particular situation. I’ve just got to worry about how does this scene resolve? How do I end this chapter? How do I phrase this sentence?”

TLDR: Just a quick synopsis on the current situation out in the Dothraki Sea