Just a suggestion, the only way you could effectively add treaties, puppets and unions would work on certain maps. I think they could make on map built around those ideas, then have them able to be toggled off for the "Europe: Clash of Nations." Same with advanced rounds.
Other ideas: I mean, this is a WWII game, so that wouldn't really fit. Also, Bytro (the creator of this game) has a WW1 game and a Modern Game on Open-Beta. Why take away from those games, a few of which are as popular as this one.