use of SRV records for apps that aren't specified to use them is a
violation of both those apps' protocols and the SRV specification.
Agreed. But it's an option for people who need to build new apps to
kludge around NATs.
presuming, of course, that the app only needs to communicate with peers
in a single addressing realm outside the nat, and the app knows what
its external address/port is, and the app is able to arrange for the SRV
records to reflect that, and the address binding doesn't change during
the TTL of the SRV records. which, taken together, is a big stretch.