Problems only exist if people use those nicknames to impersonate anyone else. If there is nothing like that, I see no problem.
Prohibit anyone to use a specific nickname is unfair, and you can imagine as well as expand to a bigger scale like there are many forums, not only Bitcointalk.org or altcoinstalks.com. Don't only limit to these two forums and think like if two members in two forums have a same username, person behind those accounts is one person, or one account is an impersonating.
Well, I have explained myself in that post already. But allow me to repeat myself.
If it's like a common name, I don't see any problem. This is one of the reasons people use a nickname/username for their online presence. If you search on the internet, you probably won't find many accounts if you search with the username LoyceV, theymos, or bitmover, etc. It's because these are not real names like John Doe.
I think Altcoinstalks is now very close to the Bitcointalk community. It happened after the mixer ban. All the mixers moved to Altcoinstalks, and the campaign managers moved the campaigns there. The forum members joined there as well. It's not like those people never knew that usernames like GazetaBitcoin exist. Even if it is not forbidden to copy someone else's username, it's not legit either. I consider this shady as fuck.