At this point it looks like Rafsanjani is the main cleric who is beginning to oppose Ahmadinejad. There will have to be more before they could potentially topple the ruling regime. It would be ideal if Khamenei would step up to the plate at this point, but it seems doubtful right now.

An internal power struggle could possibly lead to a peaceful revolution, but more likely a violent one.

A regime change and/or a destabilization of Iran would be welcomed by the west.