Feature was implemented and is enabled by default.

By default we have Use public STUN servers option enabled in the Advanced settings, which allows usage of public Google and StunServer.org STUN servers if no STUN/TURN are advertised by the XMPP server (or if server does not support XEP-0215). This way we should easily migrate to STUN/TURN servers providers by the XMPP server providers while still allowing users without this feature to make call using public STUN servers.

If this option will be disabled then WebRTC will only use STUN/TURN servers advertised by the XMPP server and if no STUN/TURN server would be provided then it will need to work without it (most likely will fail).