But wouldn't you have to wait until you sign up say, 100 or 200 people to build a reasonably dense apartment building? How is that going to be practical? A co-o

But wouldn't you have to wait until you sign up say, 100 or 200 people to build a reasonably dense apartment building? How is that going to be practical? A co-op is then going to have to run on consensus about what sorts of amenities to build, and what to do with common spaces, etc. Another question might be: there's nothing stopping anyone from doing this now. You could go start one of these at this very moment if you wanted to. Why do you think it hasn't been done?