The current assumption is that Revenge of the Mummy will be sentenced to eternal death to make way for Diagon Alley, but the only problem with that is that Florida's layout for Diagon doesn't exactly fit alongside the mountain. You can make it work, but you have to essentially pivot the entire land clockwise along the entrance of Gringotts.
Lower Lot 1 by
David Daut, on Flickr
The upside of this layout, at least from the studio's perspective, is this minimizes the number of sound stages that would need to be demolished and (assuming Transformers gets a new facade and the Studio Commissary is bulldozed) eliminates the backlot aesthetic that is no longer en vogue. The downside is that it boxes in the Lower lot, leaving less room for future expansion. There's also no room for King's Cross in this layout. You could fit the station itself in the dark grey area to the right of Diagon, but good luck finding a way to get people back there.
However, there is another way to make Diagon fit on the Lower Lot, and even in a way that maintains the original Florida layout:
Lower Lot 2 by
David Daut, on Flickr
In this version, you lose an extra four sound stages, but you have room for a larger London courtyard, and King's Cross Station, albeit a version that's scaled down from its Florida counterpart. This also preserves Revenge of the Mummy which provides extra ride capacity in the short-term and additional expansion space for the future (you tear that sucker down and you could easily fit another SLoP-sized ride, some shops and restaurants and still have room to spare).
As for Nintendo, I have to assume it's going to be
at least as big as Diagon, which means you're losing nearly all of the sound stages on the front lot. I have no idea where the studio is going to relocate that much essential production space.