XMPP is wildly extendable, my limited understanding is that Jingle is the extension used for this. From the abstract:

This specification defines an XMPP protocol extension for initiating and managing peer-to-peer media sessions between two XMPP entities in a way that is interoperable with existing Internet standards. The protocol provides a pluggable model that enables the core session management semantics (compatible with SIP) to be used for a wide variety of application types (e.g., voice chat, video chat, file transfer) and with a wide variety of transport methods (e.g., TCP, UDP, ICE, application-specific transports).

I haven’t seen anything about the the extrema of the use cases like that, but Movim is working on building out many of the features of discord and it is built on XMPP.