In Sitecore 9, does Federated Authentication improve the performance limitations for persistent users? It appears to wrap around .NET Membership, which is the same as previous versions.
(Credit goes to Jeroen de Groot for the question)
As a note, user persistence is optional with Federated Authentication.
Federated Authentication supports both virtual users and a membership-backed user. It is also possible to roll your own persistence if required.
Since the underlying Membership storage structure is unchanged, the same scaling limits apply as with previous versions.
NOTE: The official documentation site has an article on how to configure persistent users.