I hear you, and if you want something, where you know before, that it’s not the best solution, that’s fine! It’s more about an informed decission. If you’re good to go with that level of reliability, that’s fine!
But don’t overestimate this. Google put these restrictions in place, to avoid people tracking other people, aka stalking. And that’s why this system is not really reliable for tracking, you just won’t know, when the tracker works. If your “quota” was exceeded, you might not get an updated location for hours…
Anyway, I can see your point, but what I really don’t see for now, how this would be useful in HA. It still seems to be something, that is more useful in an app, where the receiving end can move with the device.
The thing is, to make something like this work in HA, you’d need a good use case, that fits the goals of HA, and I really doubt, that this is one of them. Only the mentioning of stalking is something, nobody wants to be associated with.
And to be fair, Google would need to play along, what I doubt as well. They will set some boundaries on how often you’re allowed to ping or search for a device, and if that’s to often, they will block further execution.
All this, and I can see why nobody wants to get their hands dirty with this. It is a lot of work, Google will likely try to limit you as developer and it is not really a function, one needs in HA. Issues and support questions will likely be a nightmare, as a lot of people will ask “why does this not work like this”, “why is my tracking off for hours” and such.
So in the end, I personally think, this FMDN is quite overrated, especially it is not sold under the correct name. It will not be a reliable tracker, it will be much more like these old keychain beepers, that reacted if you whistle…
As I said, it’s not that I would be against it, I just don’t see any real use case, that fits specifically for HA. I can see use cases, that are already well taken care of, eg. an app.