Fire Emblem Musou.

I'm not sure I care, as long as it's more tactical than the recent games. Back in the PS2 era, the games used to be actually tactical. Now it's almost irrelevant where you go and what you do, you determine the outcome of the battle alone, as long as you don't let some crucial objectives fail. There's no meaninful tactical freedom anymore. I know there's Empires too but it's not the same.

As for the setting, I love Three Kingdoms and I don't think I'm ever going to get tired with it. They still haven't even expanded the series to the full timeline, I think! Basically it all seems to magically end with the defeat of Shu, almost completely ignoring Wu. Yes, it's mostly wrapping up loose ends. And yes, it does matter. It took Jin almost 20 years to conquer Wu after the defeat of Shu. It simply can't be ignored.

As for other possible settings, I don't have any specific ideas. I guess I'm open to different ideas, as long as I have some interest in the setting (e.g. I don't have any interest in Gundam, so I'd probably never play those games).

Sadly we know how much Konami loves using that franchise. 

Fairy Tail? Natsu would just scream something about friendship and all the opponents would fall down.

My choice is K-ON.

A week ago I would have said "NBA," but now the Warriors are looking (relatively) mortal, so....

That's not a problem. They will just include him and the main char of FFXVI after they rename it to FFXVII in 2025.

Id love a Final Fantasy warriors, Koei are already doing Dissidia and did DQH Id love them to do a Final Fantasy one now.

Fire Emblem Warriors!
And for something a little crazy, after seeing the villager in smash, I want Animal Crossing Musou. Make it happen!

Youkai Watch Musou. I've got a feeling we might see something like this, considering Level 5 loves to mix this IP with everything it can.

Star Wars! Play as Darth Vader running around with your army of storm troopers.