I think something different might be going on. It's a hunch, but there's reasons why I think it. We know a bit about how the game is being updated with things like going to DX11 and 64bit, but I think there's more happening in the game logic we don't know about. The beneft of changing out the game logic is they can retain all of the expensive visual and audio assets they've made, and keep their TS4 player base intact without any risk of trying to sell us all a new game, but it's not the same old game inside the code any more. I think we're geting a sort of hybrid TS4/TS5 in the end with existing assets and new game code.
I really get what you're saying about the shells. I love most the TS4 worlds, but also want more control over how they look and feel.