Pretty much all XMPP software supports mentions by scanning incoming messages for... well, a mention of your name.

XEP-0372 (your second link) is a way for sending clients to more explicitly mark mentions in a message. Clients are gradually switching to this instead of the text scanning technique.

The first link you gave is to a proposal in the inbox (it wasn't accepted), and the third to a relatively new proposal that is mostly for servers to help them know when to send push notifications to offline users in a group.