As of right now, the Big Book is going to consist of just new material, with a few revisions of older stuff, but we had considered just doing a combined version. The problem with that is that, not only would the layout guy have to go through the whole thing all over again, but also people who have already printed out the first part might not be too eager to print all the same stuff twice, since the new stuff would be intermingled with the old. If a whole lot of people say they'd rather have them combined, though, we could do it.
As for a due date, it's looking like the end of October, or the first week of November. We have to finish everything for the print version of Tournaments, Fairs, & Taverns by October 14th, so at the moment, the Big Book is second on my list of priorities. Hopefully I can get TFT's text done by the end of this month, so we can start piecing together all the stuff for the Big Book of Super Powers.
And remember, your feedback and requests are definitely appreciated.