If I was happy using my Google account everywhere, I would probably also be happy with Google Groups.
Why not use something like Mozilla Persona for authentication instead? That way, you're not automatically excluding people who don't have Google, as well all the benefits concerning privacy and vendor lock-in.
We're definitely working on adding additional ways to authenticate. Right now, we're using Google because that's something most people have. We're trying to make a much easier user experience than Google Groups, so that's why you'd want to use ZeroMailer.
Why not use something like Mozilla Persona for authentication instead? That way, you're not automatically excluding people who don't have Google, as well all the benefits concerning privacy and vendor lock-in.