Really. Remember the retention pond used to be where Space Mountain now is. It is designated to be built on. Here is the never realised 1980 Tomorrowland phase three proposal:
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Plus there's the management lot (that they stole from the theatre)
Other "easy" designated areas are north east outside the berm, and behind BTM (once again outside the berm and beyond the canal)
The small space between the CP and Treehouse (originally planned to be an Adventureland restaurant connected to the CP kitchen complex) is really beyond use now with backstage and JC maintainence. There is space south of the PoTC show building but it'd need an Indy style access arrangement. South of Splash you have AVAC and parade storage making it not that viable. Long term there's north of Fantasyland but that area is not easy to build on since it was never properly prepared for use.
If anything Tomorrowland has the most designated expansion space in one land.
Thanks for the explanation! I mentioned the parking lot (old theater area) in my original post and still hope it'll one day be an extension of Main Street and connector to Tomorrowland. a connector there would really help congestion along Main Street at parade and fireworks times. A New Orleans Square expansion would be great for the area.
So, is the area north of SM usable? It seems like it would be perfect for expansion.