I'll once again throw out the idea of using GitHub organizations:
- outsources name registry to another system
- outsources antispam to another system
- outsources organization membership to the system which is already the IdP. In for a penny, in for a pound
Domain names buy you the first two, but given the existing GitHub IdP integration, the third issue is the big one for me. Using anything but GitHub for this purpose will involve building a complicated organization membership management system into crates.io. GitHub nicely avoids that.