Hey /vp/! I had the opportunity to try an unfinished version of Pokemon Sun for testing, and I am going to tell you all that I know. I couldn't play much of the game, only about an hour of it, but I can tell you what the new feature/gimmick of this gen is.

Hold on to your hats people........its a "fifth move"! I put fifth move in quotes for a reason. So you know how Kukui researches Pokemon moves? Its because of this new feature. The fifth move is not un like the burst attacks in Pokken Tournament and can only be activated by filling a gauge that fills up from battling a lot. The new diamond stone things are required to have in order to use this special move.

Its actually kind of cool, and doesn't seem like something that will ruin the games. I don't know if it is possible to use the move in multiplayer as I didn't get to try multiplayer.

Pic related, it's Pikachu's special move.