Well , there is a 4-chan leak that that claiming itself to be Chinese leak--
http://boards.4chan.org/vp/thread/33027660/ultra-sun-and-ultra-moon-chinese-leak
The first leak --
>29 new pokemon, of which 3 will be legendary/mythic
>2 new ultra beasts
>there are 5 gyms and 3 trials, the pokemon league stays as it was in sun and moon except for acerola being replaced by a new member of the elite four
>postgame will include catching ultra beasts and the battle tree but will also add 2 new small islands for a story similar to delta episode and this is how players will obtain marshadow
The second leak claim to be real leak --
>you can chose between trials and gyms
>you can change pokeball of your starter
>there's a shop where you can create customized pokeball for your starter
>move tutors including new ones, more tm's
>cross will be new champion
>dragon trainer will be elite 4
>hex maniac story from XY will continue in surprising way
>sycamore will give us mystery egg with random shiny starter from past gens
>sycamore will hint us return to kalos [which will happen during next gen]
>alola starters will receive mega stones and new ultra Z movies [same for other special pokemon]
>the story focus more at ultra beast's and you will have to fight them during the game to stop necrozma [you cannot catch them until post game]
>solgaleo and lunala will be another kyurem fusions
>guzma will have a surprising role in the game
>battle tree is now more popular and resembles PWT
>pokemon amie/refresh is now even more advanced, and your interaction with the pokemon has been expanded
It felt possible until he mention Cross being the champion and Alola starter having both Megevolution and signature Ultra-Zmove,