Multiplayer and roguelike are two ideas that aren't casually reconciled.
Turn-based facebook games are interesting, but they are likely to contradict the enjoyable parts of playing roguelikes.
In a roguelike, there is no distinction between salient actions and arbitrary ones. That is, which actions are significant?
In facebook games and other turn-based games, we divide turns into salient actions, those that effect gameplay significantly. In a roguelike, there isn't a clear measure as to when a player has performed enough actions that are satisfying- that is, each turn may or may not create incentives to continue playing.
If you can perform X such and such actions per turn, there is no assurance that those X actions will result in a satisfying game session or result in a significant amount of progress. Then you just have to wait until your friend takes his turns.
The question is- how do we break up the turns? A single level is a natural breaking point, but there isn't much room for multiplayer interaction turns are levels. A genre whose coherence depends heavily on discrete turn-taking isn't going to easily translate into the facebook arcade of games.
It's a challenging problem.