From what I understand the author JK Rowling is very involved in the planning of this area. If she doesn't give the go ahead on any part of the theming it doesn't happen. They probably could have "worked in" the Oak Tavern ( it did look pretty cool) but I think HP fans that go to this area when it opens are going to be the most critical of it. If something isn't right or doesn't quite fit, they are not going to be happy. This area is going to be something that brings guests in that wouldn't venture to IOA/ Universal(my family for one) otherwise and the hope being that they will like these parks so much they will have reached a once unreachable audience and turned them into fans of their parks. Trust me if this area is done "wrong" by not theming something just right, the new guests won't come back and the IOA veterns who are also HP lovers are not going to want to see something reused just for the sake of it or because it could possibly fit the new theming. Anything that is left is going to have some major retheming I am sure.