I know.
And the mechanical bits would take up twice the space.
By the look of it, the mechanical parts require a bit less than the smallest diameter of the disc, so it would simply be a matter of having vertical distance below the floor, and overhead. There would, of course, be the niggling detail of having a roof over it, whether small or large. Getting a roof to do what that tabletop does would be SO trick, but would likely quadruple the cost of the project. Walls would, I think, be comparatively simple arrangement of overlapping sliding segments that separate to reveal additional interior and exterior panels as the room expands. Operation would be similar to how a typical sliding van door works.