While I think it would be cute to have a meeting and greet with Anna, Elsa, and Olaf together, I kind of doubt they'd do that because the proportions are wrong. Disney seems to try and keep things as "realistic" as possible (e.g., you're supposed to be shrinking when you go meet Tinkerbell in Pixie Hollow), so I doubt they'd combine them into a single meet and greet. My guess is that Olaf will move to the Animation Building, but be in his own meet and greet area. Either that or maybe they could move him back to the old A&E m&g areas in DL (by Pinocchio). I know they use the Snow Fest building for private events, staging areas for the music groups, and it used to have a character dance party.
