What seems clear is that he's putting himself out there as the opposition's leader, and its public face. He wouldn't be doing this if he didn't feel he had enough support behind-the-scenes to survive a backlash.
I can't really see it as an encouraging development though. Rafsanjani is more likely to co-opt the opposition, and try to fold it back into the system, than he is to help push things towards the (inevitable?) collapse of the Republic.
If Rafsanjani tries to steer the flood, he's going to be pulled under. The best he can do is try to surf the crest, and land in a position of power when it sweeps away the old power structure.