I think it's time for me to be brutally honest with this theory, I hate it. Like it's one thing to make theories for fun, but I don't understand this theory at all that is never going to happen in the first place, since it's more of a meme and has a lot of weak points and doesn't have that much proof other than just sharing the same personality or mannerisms. Which in my opinion, they also had some clear differences and what I also don't understand is why some people are against the idea of the MoM being his own character. Is it wrong to come up with a new character design, with its own identity, backgrounds, etc? How about for once, introduce a new face since we are about to head into the new saga.

I know we don't know everything about Demyx, but you have to realize there are other ways to reveal his origins without him being the MoM, and who knows, just like Luxord who showed up in the recent KH4 trailer, it's only a matter of time for Demyx to show up and reveal he is from Quadratum as well. And even if he is not from Quadratum, there are still other ways to reveal his origins that he could be a Keyblade wielder from a long time ago maybe in Scala ad Caelum from Missing Link era or a different timeline from a long long time ago before the events of KHUX and it's actually kinda weird that some people haven't thought any of this yet for KH theorists. 

Like I said, you can definitely come up with any theory of who the MoM is. If you think he is Sora's mom then hey, you just solved the mystery on why Sora haven't come back with his dinner yet lol. However, if you ask me who the MoM is, he's a new guy. Besides do you really think Nomura is dumb enough to pull another same reveal with Xigbar as Luxu?

I hated the Demyx is the Master of Master theories, and I don't understand why people are still believing it.