For end users, all that extension stuff is not in their hands, hence only a solution in the wikimedia core can help reliably. Example use case leading me to this ticket: On some sites (not wikimedia ones) I have 2 users because of historical reasons, e.g. 2 wikis were merged and in both I had an account. I simply want do merge my two accounts into one or alternatively deactivate/delete one of the two, so it's having no login, edit or whatsover functionality. I simply do not want to have to care about the disposed account any more and even after leaking passwords, that account cannot be taken used by bad boys for any action.
I'm for sure not the only person having such situation, so please add some solution into the core in order to keep the user base of wikis clean & reflecting the reality. Thank you :)