That's already a thing in many online games and forums, so yeah definitely.
I have hoped for this, actually. I have a very very common last name, and can't ever get an email address or username that doesn't have to include many random numbers. I would happily pay for a simple username.
We already do
I can't sell mine until I speak with my copyright attorneys.
this is already a thing
Thankfully it hasn't really come to pass - yet. If I recall the really early user accounts on Slashdot.org were 4 or 5 digits and they seemed to have some prestige... maybe a few of them were sold. But its never really been a thing.
There was an episode of the Reply All podcast that discussed this exact thing: https://gimletmedia.com/shows/reply-all/v4he6k
can't think of many screen names good enough to sell or buy, it is easy to come up with something free