The recommended minimum for confinement, where they're in the coop all the time, is the same as for a run, 10 sq. ft. Most of the time it doesn't get mentioned, because most people don't do it. Most people use a smaller coop and then 10 sq. ft. in the run. I agree that if you're only going to give them 2 sq. ft. per chicken 24/7 you're going to have to debeak them. It wouldn't be much of a life for the chickens, either. If you give them more space, then they'd have more room to move and you could set it up with some platform areas and windows, to add some interest, light and keep them busy.
