If you could get certificates for them, so could anyone else including your adversaries, since there is no system of ownership for them. It would be like issuing certs for https://192.168.1.1

Actually that's why browsers already treat http://127.0.0.1/ and certain other local IPs as if it was via https.

For all local IP and domain space - that is 192.168/16, 10/8 and so on - it should automatically treat them as if they were safe anyway.

They're likely be part of a cafe/hotel/guest wlan or a poorly managed "intranet" full of vulnerable stuff that needs to be shielded from CSRF. That's in addition to having ambiguous addresses. So should definitely be treated as less safe.