I'm the mod over at team_up so of course I'm going to be biased. So I'm not going to tell you that the game is teh best game evar, lol or anything like that. I will just say, yes, we've been active since May 1. We just added eighteen new playable characters and in the past two weeks we've had a surge of new memberships, but we've been going strong for seven months now.
The game has a focus on threading. The rule is really "write as little or as much as you want, just give the other person something to go off of." We do use journals, but we also have a lot of threads that don't usually take two months to resolve. We have a lot of character interaction plot, ships, etc, but also some big game wide plots (ranging from angst-ridden anti-mutant crucifixions to silly Scarlet Witch accidental spells).
As for your question, right now we have a few characters left from our "most wanted" survey I took a few weeks back. People were looking for Mystique, Hellion, and Beast the most. After that we would like Johnny Storm, Psylocke, Pyro, and Cannonball. I would love to see an Omega Sentinel for some plot I have planned and a Doc Samson to shrink the heads of these screwed up kids.