What I had expected has come to pass: Rafsanjani has convinced the Assembly of Experts to have an emergency meeting.
As I've said innumerable times, this is the primary battlefront. Eighty-six clerics will probably decide the fate of this. The Assembly's only job is to evaluate, instruct, hire and (if necessary) remove the Supreme Leader. If they're meeting, that's what this is about.
If they indicate to Khamenei that he is in danger of losing their confidence (the most likely scenario), he will have to either leave Ahmadinejad twisting in the wind by calling for re-election or at least force him to call off the Basij...which amounts to roughly the same thing. If they just sack him, then Montazeri will probably be the next Supreme Leader, the reformists become ascendant, and the world will quite literally change overnight.
If they give him a pass, then that will be the tipoff to both Khamenei and Ahmadinejad that they enjoy clerical support, and the protesters will have a much more difficult struggle ahead of them.
But Rafsanjani leads the body, and if there weren't a problem, they wouldn't be having this meeting. So that latter option is unlikely.
Personally, from what I understand of Iran and Khamenei, it may be that the country would be better off with another leader. Removing Khamenei would be a signal that the Supreme Leader is not omnipotent, and lead to more careful, discerning head clerics in the future, ones who recognize that they are not the Republic.
But, as always, this is Iran's story. This is their choice.