On the World War I topic, I don't think it would be hard to create a compelling and exciting game, people think that the overall strategic stagnation reflects tactical stagnation, which is a grave mistake. It is this period that saw the birth of modern squad tactics.
The last years of the war witnessed the development of stosstroopen and shock combat, and let's not forget that the Eastern Front was NEVER stagnant and rarely bogged down to trench warfare. About weapons, there was a plethura of different pistols and (hunting) shotguns available, especailly to officers, not to mention brutal hand to hand melee. If pistols were redesigned for better accuracy and stopping power, and a complex hand to hand system were added, complete with hand held bayos, shovels, etc, I think it would be quite intense. I also think such a game would offer the best possibilities for teamwork we have yet seen.
BUT AGAIN: I would really love to see a game on 1) the Boer War 2) the Russo-Afghan War (but I'm sure TW has already decided what it's doing, and this entire thread is useless ;-)