Hmmm, good Q @marcin!
There’s nothing stopping that at the moment, for sure.
It would be a pretty bad choice for a public name (a xor url exmaple: safe://a078516207e36aa2371e17750c93276446bdb4867c027035531b89430aa8d3ae2fa4dbb59 from the proposal post ).
One possible thing is to alert people to this when making a publicName (of given length/style or some such), but that’s not a real solution.
I’m not sure what we’d need to do to prevent it (nor if we should be, given how edgy / terrible that is for a public name… which if you’re doing that, why not just use the xor url?)