Eric,
Actually, there are some SIP servers on AMPRNet already; and I'm capable of standing up a SIP server at my station. The only problem personally is that there's not much of a reason to stand up multiple SIP servers. Even if we did, it would be a good idea to standardize the call scheme to interconnect them, so we could dial those with SIP registrations on the various servers.
Regarding announcing services:
What exactly do those who want services announced wish to accomplish by having services announced over the network (and to the world if added to the DNS)?
My idea was more-so that those who don't mind informing the AMPRNet at-large that they have a service to share (and don't mind sharing that information) could post it to the list.
-KB3VWG