For me it’s simple: a practical sets version of Soarin, using the same ride system as Jurassic Flyers in Beijing/Arthur at Europa (simulating eagle talons). You would fly over and through all the most iconic locale—Rivendell, Moria, Isengard, Argonath, Minas Tirith, the Black Gate and of course Barad-dur/Mt Doom!
The entrance would of course be Bag End and would transition to the woods where Gandalf leaves Frodo and Sam, where guests would board. However, idk how to hide a show building here, unless Bag End is actually on the second floor. I also don’t know how it could be made ADA friendly.
The unload would have to be a separate environment, likely simulated to be outdoors to make going back into the Shire feel more natural. Throw in Green Dragon restaurant and wa-la!
Idk what a good theme for a gift shop would be, though? Maybe Bag End could be both the entrance and exit for the ride in the same way that the Ministry will be, and therefore it can be themed to things Bilbo and Gandalf may have collected on their adventures? Of course, that could create a logjam of people going through the door unless you supersize it beyond the realistic scale. All else fails and Sam’s house being the exit works fine.