"...if you have an Apple silicon Mac and AFP support is dropped from macOS 27, that would leave you unable to upgrade without replacing your network storage."
How big is this market? I'm not saying vibe code a product, but...
Netatalk has been around for like 25 years: https://github.com/Netatalk/Netatalk
Relevant to the discussion is that the project comes with an AFP client as well. I have no experience with the client but I've used the Netatalk server for more than 15 years.
That "replacement" is not always full-on hardware.
I have colleagues who are running AFP on BSD for continuous backups on their systems, and they have to reconfigure something new to be able to continue backing up their systems.