Well considering the rumours for this are saying it has two floors I suppose they'll be using up a fair amount of space but, yeah, just what are they going to fill all that space with? Even with two floors that seems way too tall.
I always get a little sad when I check this thread. I used to live in London and visited DLP every few months, and I would have loved for the Ratatouille ride to get funding a few years ago so that it would have been open while I was still there. Can't justify a trip to Paris just for this ride, but I would have loved to experience it.
The former costuming building (used to be part of the studio tram tour) will be reskinned to fit with the parisian look of the area, and will host fastpass for the attraction and toilettes. A shop is rumored too, but not yet confirmed.