A few years ago you upbraided some developers for not following the correct process when requesting a reserved network port from IETF (Internet Engineering Task Force). While I get that squatting a used port is poor practice, I wonder if you, yourself, have ever tried to get IETF to allocate a port. We recently went through this with a new protocol on an open source project, and it was a nontrivial and frustrating exercise. While I would not encourage your readers to squat ports, I can see why they might just look for unallocated ports on their own and simply start using those, with the expectation that if their protocols proved popular, they would be granted the allocations later.
Funny you should ask this question at this point. This summer I, too, requested not one, but two ports for a service I had been working on (Conductor: https://github.com/gvnn3/conductor). I have always been annoyed there is not a simple, distributed, automation system for orchestrating network tests, so I sat down and wrote one. The easiest way to implement the system was to have two reserved ports—one for the conductor and one for the players—so that each could contact the others independently without have to pass ephemeral qports around after they were allocated by the operating system during process startup.