I'm not sure if anyone has reported on this yet, but from what I saw on my visit today they yet again changed the window displays at the Universal Studios Store to carry the 25th theme. Each window display is now themed to each of the park's original attractions, featuring plaques commemorating them, various photos and merchandise items relating to the attractions, and the UO 25th logo in the background.
Each window is themed to as follows:
Kongfrontation
Back to the Future: The Ride
JAWS
E.T. Adventure
Universal Classic Monsters
Ghostbusters Spooktacular
Alfred Hitchcock: The Art of Making Movies
It might not be the exhibit/mini-museum everyone was hoping for, but it's defintiely something.
I sadly was not able to get any photos as I was in a bit of a rush (plus I'm also pretty terrible at that sort of thing), so hopefully someone else here can.