If I can use my DHCP assigned IP, will this allow me to drop having to use self-signed certificates for localhost development?
No, they will only give out certificates if you can prove ownership of the IP, which means it being publicly routable.
Browsers consider ‘localhost’ a secure context without needing https
For local /network/ development, maybe, but you’d probably be doing awkward hairpin natting at your router.
What's stopping you from creating a "localhost.mydomain.com" DNS record that initially resolves to a public IP so you can get a certificate, then copying the certificate locally, then changing the DNS to 127.0.0.1?
Other than basically being a pain in the ass.