@prologic@twtxt.net I had to do some research for this one. The answer is yes, in theory, as long as the client or server supports XEP-0368. However, this seems like the kind of thing that would be skipped by lazy implementations. I would be interested to see how this looks in practice.
SRV records are used in the XMPP core specification to determine the domain and port to which clients and servers (for s2s connections) should connect. XEP-0368 is an extension to the spec detailing how servers and clients should handle SRV records in relation to TLS connections. It says that the “Client or server MUST set SNI TLS extension to the JID’s domain part.”
As an aside, SRV records alone can be used, in theory, to change the default port used in c2s or s2s connections. If the ports were assigned randomly from the hosting provider, they could be specified in the SRV records and everything would hopefully just work. Again, I don’t know how well this is supported in practice.