[Johnnynator]

> Shibboleth is the last major IdP I know if that is SAML-only

Shibboleth has officially supported Plugins for OIDC for some time now.

As others said, Shiboleth is still rather pupular at Universities and higher Education, OIDC will have a hard time to set foot there without the OpenID Connect Federation Draft beeing finished and then Implemented by the different Metadata Federation that exist (most National Research Networks manage one)