Word on the street seems to be that the bulk of PE megafund associates have received invites, which suggests that the bulk of people who'll receive HBS interview invites have already received them. Not to be pessimistic, but if you look back at last year's thread, there was a lot of fuzzy, optimistic thinking very much along the same lines of this year's thread comments, so I'm skeptical (but hopeful) that this year's Wave 2 will be sizable.
Based on last year's thread, it seems like best way to know how big Wave 2 will be is to ask those who've received invites roughly how many "spots" were up for interview when they signed up for times, but I don't know if that is easily visible this year. In any case, as the wiser folks have noted, this is all pointless speculation that doesn't actually increase our chances tomorrow.
Good luck to everyone!