It won't be Gaga, pretty sure her announcement was intended to prevent monsters from getting their hopes up (but knowing how they twisted the "3 betrayals" thing in the past, she should know she wasn't quelling anything).
Looking at the replies in here, I realize I have no idea who Tori Kelly is.
I'm with the few posters who don't want it to be Katy. Rise got boring fast, tbh.
Best bet is... Bey? I'm ok with that.