I think we'll see seasons again, if not with Sun/Moon then eventually. I think it's the natural progression to a day/night system. Judging by the way some Pokemon evolve EVERY generation (especially with the actual scientific idea of evolution and how it works), and how most regions tend to have a single location with much different weather than the rest of the region, it seems like they've been playing with different ways to implement seasonal weather; it's just not a priority feature.
The games could use a more time-lapsed way of showing progress so it doesn't feel like the whole Pokemon League took a couple of days in-game. I'm sure they're just waiting for a console that could handle changing seasons, a region where it would make more sense than Hawaii, and a better way of implementing it before they make it a higher priority feature.