I've been kind of mixed about this myself.

Keeping certain mechanics to certain games (and their subsequent rereleases/remakes) make those games more unique in their own ways. And then, of course, there's the pandering in the live service spinoffs like GO.

But at the same time... yeah, I'd like to see certain mechanics come back. I don't miss Seals (or Contests, really), but I wouldn't be against Megas making a surprise return someday.