If publishing from ArcGIS Pro is going to continue to be available only to a federated server (through Portal), then we need that server to be accessible by more than one webadaptor. as it currently is for unfederated servers.
Currently, once a server is federated to a portal, it is only allowed a single webadaptor. This means that if your portal is inside your firewall, the permissions to the data outside the firewall are either complex or impossible, even if your portal has an internet-facing webadaptor. No matter what the connectivity of the portal, all the map services it references must be independently accessible to the map or application, and that means they need an internet address, not an intranet or network address.
For security and stability reasons, we will not put our ArcGIS Server outside our firewall. Trying to federate between a server inside and a portal that is either outside, or has a web adaptor to outside is either difficult or impossible. (I worked with tech support for 3 weeks trying before we all gave up on it.) When unfederated, our server is accessible through a webadaptor outside, and one inside, and everything works great. We need that simplicity in a federated environment (even if it requires federating the server with as many portals as webadaptors.)
Alternatively, if Pro could publish to an unfederated server, then this would not be an issue.