Yeah, built-in TURN/etc. in Prosody is unlikely to happen. We believe in modularity, smaller footprint, separation of concerns and the "do one thing" philosophy. Coturn is a decent battle-tested TURN server and works just fine :)
Rather than trying to reimplement stuff that other projects have done quite nicely, we're focusing on trying to grow the community, network and ecosystem with projects like easy onboarding[1] and Snikket[2].
[1]: https://blog.prosody.im/great-invitations/ [2]: https://snikket.org/