@jec @DawnPaladin You bring up a very important point: DNS is a big problem. Domain names are inherently scarce and therefore expensive. This adds to the already large burden of self-hosting.
It's a big reason why people end up with big-social-site.com/@my-username: because it's free.
We should ask ourselves how this can be addressed (heh). How important is it to have a globally unique human-readable name online? Pretty much none of us have unique given name + family name, yet we manage fine.