I was playing around with the dimensions of the DL vs WDW show building. Turns out the width of the DL version is at least 50 ft shorter than the WDW version! The WDW version, however, takes up the entire length of its show building, judging from blueprints available.
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I see two ways around this. First, the width could be reduced by reducing the number of cars per set from 4 to 3. This would allow the waterfall scene to be less wide, and other scenes at the beginning of the ride could be shrunk in the same direction with the reduced number of cars.
Alternatively, since they'd already be changing the floor plan, they could just design up a new floor plan that takes advantage of the extra length of the show building being built behind Toon Town.
To be honest, I think the former seems more reasonable. It's difficult to imagine a layout that would optimize the space for a more narrow building.
Either way, given the extra space needed for the queue and maintenance bay, the rumor that the extra square footage would be dedicated to any substantial office space seems unlikely.