I was basically joking about Gaeta. I think him being #7 would be a very weak revelation; his ultimate fate was poetic in itself, and I don't imagine that it would be undone so abruptly.
Starbuck does seem to be the candidate, if #7 still exists in some form. That, of course, keeps open the big question as to what the "Cylon god" is supposed to be. I found it interesting that Ellen tersely stated that it was created by the Centurions, and that it seems to act independently of the other Cylons. Also, it might be a decent chuckle to note that the original Starbuck back in the late 1970s show was a man; perhaps when Ellen talked about how Cavil "contaminated the chromosomes" of Number 7, it's a sly reference to this.
I tend to think that the reveal about the nature of the Cylon god will answer about the origin of the Virtual Six too. Can I say that one of the biggest disappointments of the latter half of BSG is how Virtual Six just kind of disappeared and never came back? Of course, Baltar really hasn't had much of interest since he became a messenger of the Cylon god, at the behest of Virtual Six--yet another indicator that this amorphous being is involved.
Some interesting things ahead in the show, it seems.