de0u I think its obvious that somebody would have to maintain those servers. Basically what is being asked for isn't just "google"/"grapheneos"/"disabled", but rather also add a "custom" option. From the top of my head, connectivity check, gps, updater.
Having it connect to grapheneos servers, in addition to making you vulnerable to the integrity of those servers, identifies you as using grapheneos, which is a possible risk in some scenarios, including exercising your freedoms while within surveillance states, and being able to blend in, or if authorities are looking for someone with a phone running grapheneos, its pretty easy to identify. Reboot it and see what the boot logo looks like.
Having it connect to google servers lets you blend in, but leaks tons of information about you to google, which is also undesirable.
But having it connect to a server that I physically control? That doesn't leak ANY information, because nobody can know what those connections mean.