Looking at their designs, I'm starting to get some suspicion as to their typings. And I think that, as with the B/W cover legendaries, these will have unique typings.
I look at Xerneas's legs, which resemble blades, and Yveltas's general design, and I suspect that these two will both be Fighting types. This would make Yveltas a Fighting/Flying type, which would be an unique combination. Xerneas is harder to call, but I could see it actually being Fighting/Normal, another unique combination.
If anyone wants to point out that this makes Yveltas the "superior" combination because it can hit Xerneas supereffectively with STAB, and thus wouldn't be a "great" typing setup, I'll point to Kyogre vs Groudon, which had a similar situation.







