Feature summary:
I want properly-signed (~~~~) talk page messages that mention me (i.e. link to my userpage) to send a notification regardless of the contents of the actual signature.

Use case(s):
On some Echo-enabled wikis I frequent, signatures often do not contain a literal wikitext link to the signer's userpage [[User:AbyxDev|me]]. Instead they can contain a user subpage transclusion {{User:AbyxDev/signature}} (produced by {{subst:User:AbyxDev/minisig}}, h/t T67910) or even an extension tag <signature>AbyxDev</signature>. The only consistency is that everyone signs their posts using the ~~~~ syntax.

Currently one wiki I'm on uses a hack to handle the above two specific cases, but it would be better for Echo core to support ~~~~ in the general case.

Benefits:

• Allow mention notifications to be properly sent by users with nonstandard signatures
• Depending on implementation, automatically resolves T219642 since links to other users' userpages in one's signature would not be found before the ~~~~ is expanded
• Directly resolves T67910

Resource implications:
I am willing to attempt to implement this myself, but before I do, I want to see if there are good reasons that this should not be done so that I don't waste my time.
This is of course mutually exclusive with T66778.