I just don't see it being a ride for many reasons. The shape of the building for one, does not lend itself to being a ride. Generally ride based show buildings are box shaped to maximize scene space, not elongated. Also, i have a lot of issues with them opening a tiny dark-ride directly after potter. I just don't see them taking that kind of risk. Lastly, one would think that if they wanted to go big, they would have finally gotten special events to let go of the Globe and utilize that space as well. Adding the globe would have given them a total of 30-35,000 sq feet which is comparable to the Haunted Mansion's show-building at Disneyland.
Who knows what it'll be. But I am still leaning towards walk-through attraction/exhibit.