Selfhosted

Sure, you can do whatever you want. You could even use non-rfc1918 addresses and nobody can stop you. It's just not always a great idea for your own network's functionality and security. You can use an unregistered TLD if you want, but it's worth knowing that when people and companies did that in the past, and the TLD was later registered, things didn't turn out well for them. You wouldn't expect .foo to be a TLD, right? And it wasn't, until it was.

German router and network products company AVM learned the hard way that this is a bad idea. They use fritz.box for their router interface page and it was great until tld .box became publicly available and somebody registered fritz.box.

Having a reserved local/internal only tld is really great to prevent such issues.

The main problem I have is waking up in the middle of the night worrying that ICANN pulled some more stupid corrupt bullshit that only makes networking worse and breaks my config.

Just look elsewhere in this thread: someone thinks that using .honk as a joke is safe. But what about .horse? .baby? .barefoot? .cool? (I stopped scrolling through the list at this point but you can see how arbitrary and idiotic things have become.)

Shit, let's hope the ICANN cops don't find me out then... I've been using it for years!