[cespare]

> Requires a domain name to be the first part of the module identifier

This is only true if you want the module to be publicly 'go get'-able. Private modules can be named whatever you want.

(Some tools use whether or not the first import path segment contains a '.' as a heuristic for "is this package stdlib", and those won't work correctly on a module that doesn't use a dot. There's a proposal, not yet accepted, to document this as a naming requirement for modules: https://github.com/golang/go/issues/32819 This is of course a looser requirement than "must be a domain name".)