I know this is all speculation, but here are my thoughts on what this set will include.
1.) It is 99.99999% unlikely that it will not include Day of the Doctor and Time of the Doctor. These were Matt Smith episodes, and while they include the first appearances of Peter Capaldi, there is no justification to put them in. Also, it is highly unlikely that they will publish the two together. Unlike the 2008-10 David Tennant Specials, there are only 2, not 5.
2.) It will include the 13 episodes of Series 8. There are two things that remain unknown. First, we know that there are 13 episodes in Series 8, the question is whether or not that includes the Christmas Special. If so then I would guess that this set will include this set will include the Christmas Special. If that is a 14th episode in addition to the regular 13, then I would guess that it is then a 50.50 shot. Precedence says that the Christmas Special would be included on the following release, however proximity could justify breaking precedence. We will have to see what comes.
3.) Doctor Who at the Proms 2013: My guess would be that it is not included--unfortunately. However I go along with why the Matt Smith Specials will not be included. My guess would be that either it will be included on a 2013 Specials set (which I see as unlikely) or, what I really hope, is that it will be included on a Blu-Ray set with all 4 of the other music specials in uncut, unedited forms on Blu-ray. Although a pipe dream, I hope it will come true.
4.) Special Features: Right now all I will say is that it should include "Doctor Who Live: The Next Doctor".
5.) The main features will be 1080p with DTS-HD MA audio. While Series 5 & 6 were not this way, The Complete Series 7, Day of the Doctor, Time of the Doctor and the special set of 1-7 were all in 1080p with DTS-HD MA audio.
Any thoughts? We're so far out from the first episode that it should be fun guessing until then.