I could definitely see them doing a 6" exclusive at SDCC. I think they really want to push this new line with collectors in particular, and Comic Con is a great place to do that. As others have mentioned, when the relaunched the Marvel Legends line they had an exclusive Thor that came in a Mjolnir box and had sort of a lightning effect (and eyes), then they released a "normal" version in the first wave of that line.
If they do have a Star Wars exclusive, I just hope it is something like this where if we weren't able to attend (and I'm guessing this would fly out of stock online, regardless of who it is), are still able to get the character. Imagine wanting to get in on the ground floor of this line and missing out on one of the big guns. Still, I'm interested to see if they do something cool. I know the overall opinion doesn't seem to be a lot of excitement for this line, but I'm sort of interested (although I won't stop the 3 3/4" stuff either).