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This is a well-written and clear document.  A couple small nits came to mind while I was reviewing it, which I don't think are serious blockers to publication, but just some aspects that the editors or ADs might want to consider clarifying.

1. The document mentions compatibility with existing protocol stacks, but it's not quite clear to me what is meant by that.  Does it mean protocol stacks from the IP + UDP within OS kernels all the way up through existing multicast application code (for some specific applications?), or does it refer to just the kernel portion, or just the userspace portions?  The statement is made without an example.  It could be that everything literally just works, but it's not clear.

2. The shepherd writeup says that there hasn't been implementation, which confuses me on how the editors are so sure that this is compatible with existing stacks.  I assume there were some proof-of-concept tests on Linux/Windows/Apple/etc. platforms, but nothing seems to be mentioned.  If those tests were done and there really are simply no caveats an app developer should know about other than just the common socket options mentioned, then that would be good to mention.

3. The document has good analysis about complications with firewalls.  Another common use of port numbers is in classifying traffic for different QoS treatment.  Implications for that here seem relevant to mention.  Rules for classifying flows and assigning treatments will need to use criteria other than just the destination port in order to separate different application flows sharing this port, if they're to be given different treatments.