there are some productivity benefits, and it’s the best of both worlds. You spend time with people you enjoy spending time with, and you don’t jeopardize your friendship by going in business together
What am I missing?
What if one of your friends got a new job and now they're working for your employer's competitor? Your employer might not want you to share a workspace with them anymore. Depending on the kind of things your employer was developing, they might not want anyone being able to look over your shoulder who wasn't a co-worker.
I think that a more likely scenario would be companies renting lots of small, local blocks of office space in different neighborhoods where their employees lived, which would be limited to their own employees.
Also: Are you prepared to pay the cost of renting this office space out of your own pocket? Your employer gets a really good deal if you work remotely out of your own home, since they don't have to pay for the space. But if you're going to be asking for a reimbursement for office space that you rented, they'd be much less happy. If they agreed to pay for it at all, you'd probably have to provide a careful accounting of how much you, personally, paid and what kinds of services are included in the rent (maybe your employer doesn't want to reimburse you for free beer). Again, it would be much simpler if the employer rented space for their employees, since they'd have control over what kind of space, furnishings and services they were paying for.
the dangers. some people can well behave when others need to focus, some aren't able to. that's immensely dangerous, if you committed to paying part of the rent and suddenly you don't feel it's working for you.
the next step i see is the market pushing for high-speed internet connection even in currently underserved areas (ftth anyone?).
following that, i hope will happen is that a number of currently underpopulated zones will re-bloom.
the big if is whether remote working will stay or not.