I had a thought today.
What about a forum-based mission? Combats would be difficult, and may require real-time, but story development can be done on a forum thread/board. It's like the chess-by-mail-style of game, and might be interesting. If we have lots of time, people might put more thought into the conversations with NPCs and the actions they take.
It would be in addition to the online game I already discussed, though, not instead of it.