Like, StreetView?
So to extrapolate wildly, it seems reasonable that getting similar results for, say, real-world bedrooms, you'd need to take around 5 pics each of 2M bedrooms, and record the location and angle of the camera for each picture.
Edit: and I didn't mean to sound negative, using artificially generated rooms to develop the method is a great idea, and the next step will be narrow domain specific applications (they mention eg robotic arms) where it's feasible to automatically collect enough data for a task, and somewhere in the future we may have the data and compute to sample the distribution of real world environments in decent resolution..
https://robotvault.bitbucket.io/scenenet-rgbd.html
I think there are only 15k different rooms, rather than 2M you suggested, though!