Well, I still wanna find out about HOW and WHY the megastones work to do what they do. We can look at pokemon who probably could use evolutions because of their stats and stuff, but until we understand the concept behind it, it's still a great deal of speculation as to which pokemon will likely get one.
Also, they'd better be cheap like the FE dlc. Who knows, they may even sell off shiny pokemon sets like starters, legendaries, etc as DLC. It would have to be pretty amazing stuff to make me buy it though. Adding new areas to explore with creatures you couldn't encounter in the wild before would be likely.