And in any case, let the developers fail on this if they build 400sf units that no one rents. I guarantee there will be a lot of 23 year old research assistants or whatever who don't want roommates but want to be close to work and in a good neighborhood. I've lived in less than 500sf in a very dense urban area when I was younger and it was exactly what I needed for the time being.
I don't think research assistants make 3k a month, let alone afford that in rent...
Size wise it would be just fine for one person. The 399 one would def be too small for more than one but the others you could probably make it work with two.