I agree with you on KH3's release date, it'll be 2015 at best, 2017 at worst.
I'm getting it from the fact that the Xbox One is outselling the 360 on a weekly basis during it's first year so far, and the 360 sold about 6 million during 2006 (it's first full year), so the Xbox One should sell at least 6-7 million this year, possibly even more considering the fact that the Xbox One still has more countries to release in (360 had released in more countries by this point in the year) and a possible pre-Holiday price drop (the 360 had no pre-Holiday price drop it's first year).
I honestly won't argue with you on that because it could go either way. Still, I would find it hard to believe KH3 will sell 1m on the Xbone when most multiplat JRPGS have a hard time hitting 1m on the 360 which obviously would have had more consoles sold than the Xbone. Only time will tell.
I welcome FF and KH coming to other platforms because I think other people should enjoy great games without forking out $$$.
plz dont hate me