What factions would you like to see and would you like them to be portrayed?

Obviously we can't know what they will all be since we don't know were the next game will be and while some factions are widespread, such as the Fighter's Guild, Thieves Guild, and the Dark Brotherhood, others are more local. However what themes would you like in new factions and which ones would you like to return? Do you think they should be tie to the main quest like in Fallout 4, make it were they have little connection to it like in Skyrim, or something in between the two?