That would be a great solution. I would imagine many "legacy free" users are old GMail for Domains users who just want the same Google One functionality of @gmail.com addresses but with a custom domain.
I don't even use my domain name for anything but email anymore, but I certainly don't want to give up the address I've been known by for a dozen years.
As you can imagine, my username @gmail.com gets too much spam to be usable.
