I think they're saying that address records are part of the address-exhaustion problem. If we used SRV records instead then the port numbers become available f

I think they're saying that address records are part of the address-exhaustion problem. If we used SRV records instead then the port numbers become available for service endpoint discrimination, and this is a 16-bit space as alluded to. If adopted some time back this would indeed have conserved IPv4 address space; certainly there would have been far fewer 1:1 assignments for SSL termination, and a public cloud load balancer would be able to handle many distinct customers on a single IP address and so on. In practice there'd be some introductory issues in deviating from the well-known ports involving gateway traversal (particularly corporate firewalls), but we've cleared such hurdles before.