I hope it's not out of the scope of what we have access to.
Another mod Idea I have is something similar to Suikoden ... where you start out as a random character (NPC), and recruit other NPCs, eventually get an HQ, use ur characters to command armies vs other armies ... fight battles expand your allies ... always focusing more on the Champions you recruit rather than the armies/ army battles, yet still having armys and army battles.
I suppose what I mean is, a rather static world where perhaps it takes 1000 turns for one year to pass. In such a world all existing people's are already in existance, and all recruitable armies are already there. The only way to gain forces for your cause is to gain allies via quests/diplomacy. No "building" of troops, merely recruitment and re-equippage.
Sure you can raise taxes and squeeze new recruits from existing towns ... but that could lead to dissention or even revolt.
Your main game would be on the smaller RPG level, with a party of champions out doing quests ... yet there is also a War going on and you occasionally have to lead massive armies vs other massive armies and all ur champions have special War-leadership abilities- and these abilities increase with their level.
Not sure how possible it would be ... but think of it as an RPG with 4X elements rather than a 4X game with RPG elements.