I feel like this one is pretty predicatble just based on her appearences in TYT and Make Your Mark, but we haven't had any real confirmation yet. The brushable Cutie Mark Magic Misty Brightdawn toy floating around out there right now apparently has a little hint on the top of the box as you can see above! This wwas spotted by MLPTales on Twwitter.
Things could of course change, but has felt inevitable ever since she first appeared!