An MMORPG would a good start. You won't have to worry about graphics in the beginning and if you plan your code, you can probably separate the game code (gameplay, game rules, items, etc.) from the graphics engine. Actually, you can focus on making the game (gameplay, rules, w/e) and let other people worry about the graphics. Sort of like how KDE, GNOME, XFCE, etc, are all different front ends for Linux.
You could right the 'game' n Python, and have different graphics engines running it. That way, people with flashy graphics (KDE) can play with people who don't like the flashy graphics (GNOME), because they'd be playing the same game (Linux). (Not say that KDE is more flashy than GNOME, but people do express that general sentiment)
BTW: I'm looking into learning Python right now, and if something gets started, I'd like to help.
Now that is a cool idea. So, who is going to lead this? Less talky, more codey.