Yes, Megas are in Sun And Moon but don't get your hopes up for any new Mega Evolutions in the future.
http://wwg.com/pokemon/2016/10/21/pokemon-has-no-plans-for-more-mega-evolutions/ "Each time we make a new game, we think of particular theme and of particular elements that would work well with that game," Masuda said. "This time we have our Z-moves. If a game comes up in future that we think [Mega Evolutions] would work really well with, certainly we'll look into it, but for the minute we don't have any particular plans."
