WoW:BC was the perfect MMORPG...then blizzard went and messed up with wotlk. If they had left it fine and dandy at BC i would have stayed for ever because it was so much fun, wotlk got so boring so fast.
I think an fps mmorpg where you are maybe in an army or something, or you act as a merc and instead of clans or guilds or whatever you build up an army of other players and there aren't levels per se, you just get skill ups and to learn new skills you don't get talent trees and such you would have to do certain things or use certain movemen/key combinations or do something in a certain way to learn the skill and then you would have to repeatadly use it in the correct siutation to skill it up. Then you would get skill for your character but it would take skill to be able to do it so you yourself would gain skill.
For those that like the current quest system of go kill x monsters, go kill monsters and get x itmes, got retrieve this item etc there would be that with the merc stage when you go solo stuff, for those that like pvp or fps games like CoD the armies you amass or are part of would fill that criteria too and you should be able to start a battle anywhere you like on the map and npc's would act accordingly, so, if you start shelling a building where there a few of an army in then the npc's near and around would run off screaming, npc's near the building would maybe be hurt or killed so there would be corpses near by.
There could also be war scene sort of things, so maybe a building full of terrorists that you must clear, that is the "dungeon" sort from your typical MMORPGs. And for factions you could have say countries armies (marines, SAS etc) and terrorists.
That would be cool
Watch a big game developer accidentaly stumble onto this page now and go oh my god, that is brilliant!! and go and make the game. look out for it in the next few years and remember back to reading this