You can always manually trust certificates via various means, it's the basis for almost any corporate network, most browsers also offer a simply dialog to bypass certificate warnings.
Plus, they won't remove the functionality to manually trust a cert (Business Users would complain).
Firefox has implemented the same rules around .dev tld's as google. I use vivaldi when accessing internal company .dev domains because firefox won't let me tell it to accept the self-signed certificate.
Well, another argument in favor of not overloading TLDs for internal domains, then, and just buying an additional domain if you really want to have separate internal and external domains.