I expect mods will start popping up pretty fast to make it as hard or easy as the user may want.
Uhh... I don't think you can actually mod quest battles themselves. There are no mods in TWW that do that, despite many of the end-game ones being stupidly easy too.
From the way people are describing the final battle, you don't have to do anything to win, as the AI has to fight 3 other AI armies anyway. So it's not that it's just easy. It's to the point where you don't have to even be there and the only way you could lose that battle is if you deliberately sabotaged your allies in that fight.
You can't mod the battles. But you can mod unit stats, which will increase the difficulty.
How would that make the final battle more difficult? All the AI ally troops will have increased unit stats too. I'm assuming you're referring to how you can modify the stat cheats the AI gets when you up the difficulty, but they affect all AI troops, not just the enemy. They have to, because all the AI are your enemies to begin with. You can't temporarily change the stats on a per battle basis.
So you just end up with all the AI being more powerful and you still don't have to do anything.
-----------
I don't really care too much about the ritual stuff anyway. I kinda accepted it to be gimmicky and more like a non-replayable thing anyway.
My main focus was always on the combined campaign. That and manual control ratling guns. But since I won't get either at release, I'm pretty ambivalent on everything.