... Anyhow, gamemechanics would have to be changed in order to make playing with massive armies fun, while not making heroes useless from midgame on.
To me, it would be "finished," not "changed."
Way before we had beta builds in our hands, I had a crazy notion that Elemental could become the distant PC-game cousin of Peter Jackson's Lord of the Rings films. I wanted to play a game that had all the '4X' bells and whistles but added a functionally important and interesting character layer.
Take any of the 'epic' battles in the films (or, gods forbid, read your Tolkien!), and you'll see conflicts between hordes with individuals who are crucial to the outcomes. In the earliest parts of the story, the 'champions' were in settings far from any armed hordes. By the end of the story, armed hordes were more or less the setting but (most of) the 'champions' were still there.
But I'm pretty sure my hopes are really insane because I'd ditch all the 3D stuff in favor of ludicrous amounts of logging that enabled AIs to hold meaningful grudges against me and each other even if they were actually built to be turtlers. The barely-there dynasty system is part of my pining. The game objects in that tree could be champions or chattel. I'm still hoping that in FE they might have roles in parts of the quest system just to start. And I'd scrounge aluminum cans to find money to buy an expansion that made you need to think about how you were treating a given champion, offspring or recruit.