Change default domain for new installations from "localdomain" to "home.arpa"
RFC 8375 sets aside "home.arpa" for "non-unique use in residential home networks." and in general seems to be preferable compared to alternatives like ".home" and ".local" which have been taken for use by others.
pfSense currently uses "localdomain" which hasn't been formally reserved for this use that I can see in any current (not expired) RFC or draft. It was mentioned in draft-chapin-rfc2606bis-00 and draft-chapin-additional-reserved-tlds-01 both of which expired several years ago.
The main place this would be changed is in the default config.xml, and one additional reference in index.php. There are some other "localdomain" references in the DNS Resolver and Forwarder but they are general and may not need to be changed. Though we may want to add "home.arpa" to those examples.
There are a few mentions in the docs, but not many.