[jcbrand]

because XMPP standard supports nickname changing, which means in a context of a platform it would allow nickname spoofing

Nicknames can be registered against a MUC so that other users can't use them. See here: https://xmpp.org/extensions/xep-0045.html#register

This has been part of the MUC standard for years and there are XMPP servers which support this, so you don't need to fork.

If you want to support nickname changing and still know whether it's the same user, you can use the newer XEP-0421: https://xmpp.org/extensions/xep-0421.html