Two of the buildings shown in the concept art already exist today, which at least shows where the facades would have been placed. Here’s the concept art, the existing buildings are outlined in green and yellow:
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The green building is unchanged from what exists now. The yellow building is shown in a different style, but has the same shape and roofline.
Here’s a satelite view with the same buildings outlined:
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The blue outline for the new building shows the biggest it likely could be without cutting off backstage access to the international gateway or the tent. It’s about 50,000 square feet, around the same size as ratatouille. Even if they stopped at the road and only built over where there are trees now, the building would be 23,000 square feet. As a comparison, Prince Charming carousel is 5,000 square feet under the canopy. And Peter Pan’s Flight is 18,000 square feet. So there’s plenty of space for them to do whatever they want back there really.