I think "beyond Big Thunder Mountain" should be used for a new Frontierland, with stuff like Country Bear Jamboree relocated to there, while the current Frontierland can become an MK version of New Orleans Square (maybe called "Port Orleans"), so Tiana’s Bayou Adventure wouldn’t feel out of place.
From what I saw from D23 and now know, the whole point of the Blue Sky presentation for the project was to come up with potentials for an expansion "beyond Big Thunder". I’m not saying (and I doubt) that the areas that we saw in the concept art will get greenlit, but it gives us an idea of an opportunity. It’s just like back in the early 2000s where Disneyland came up with an idea on a potential "third gate" where the Toy Story parking lot is now. Same thing with DinoLand at Animal Kingdom.