Even if they're not in the US version, theres just so much pointing to their eventual arrival. They've both got coding in the game. They're the only ones with victory music out of the cut characters. Adding them, while it may not be with release, is looking to be something thats going to happen eventually. It might take months, but all the stuff we have now is pointing towards Roy and Mewtwo eventually becoming downloadable.
Heh, now I'm half expecting each region to have two exclusives and the other four downloadable
(Japan getting Ike/Lucario, NA getting Roy/Mewtwo, PAL getting Plusle+Minun/Dixie)