What do you think are the chances of megas being in this game?
Considering just how much hype and marketing Game Freak has put into the return on mega-evolution it'd be pretty strange if it were just suddenly dropped again after only one or two years since Z-A. (I know that it's in Champions, which will probably be supported for generations to come, but that's not quite the same...)
Now I'm not saying that I think it'll be the primary gimmick of Winds & Waves (especially since the icon isn't in the Japanese logo), but I can see them doing something similar to how it was handled in Sun & Moon, where it's a secondary postgame gimmick instead. Plus when the inevitable DLC gets announced, it could have a larger focus on mega-evolution compared to the basegame, and thus would be the perfect opportunity to introduce even more megas.