I say in no way should anyone expect a Diagon Alley announcement tomorrow.
Sorry for the double post, but could this tweet link to a new attraction coming to Universal? https://mobile.twitter.com/FantasticBeasts/status/744877673827033088. Could this be one of the things they anounce if the video tomorrow?
I'm thinking we're not getting Diagon Alley, and instead will be getting something from Fantastic Beasts. A Wizarding New York, or something. All the pieces are falling into place.
Theoretically, a Wizarding New York could fit in right near the existing NY shopfronts, take over the space of Cartooniversal and Waterworld.
If you really want to go hogwild, imagine building a new theater on the surface lot in front of the globe (or alternately near the opening next to Johnny Rockets), and bulldozing the original theater. Replace with smaller shops on Citywalk side, show building for main ride on the park side.