Account Deletion - @mentions and Quote Headers

Has any consideration been given to the deletion of usernames from @mentions and quote headers when closing accounts and the member wishes their content anonymized and marked as being by 'Guest'? I understand that there might be some technical hurdles to this, but I am not even sure if their retention is GDPR-compliant given that usernames are considered PII.

'Technical barriers' are probably a legitimate defense for these omissions. But how much of a technical barrier are they? And if the barrier is low, is this a legal/legitimate defense for their non-inclusion?

I think there is a grey area here. At least in the mind of the individual wishing to close their account and anonymize their content.* Retaining usernames in @mentions and quote headers increases the pressure to remove actual content to remove instances of their username.

There can be legitimate and compelling reasons for all instances of a username to be deleted. Attempting to do this for plain text mentions surely would be more difficult and server intensive, prone to false positives, and surely onerous. However, there would be potential ways of achieving this programmatically for @mentions and in quote headers.

And there is another problem. When an account is deleted, the username becomes available for re-registration. This will give the appearance of old @mentions and the username appearing in headers as referring to the new member. This is far from ideal. There is a third-party app which automatically adds deleted usernames to the username registration block list, but that might not be GDPR compliant, as it is the deliberate retention of PII. Tricky, innit.

Any thoughts?