We are still pursuing this as well. If you have a support contract, please contact Rancher Support and ask for this feature. It will help them to prioritize the feature appropriately.
In Rancher v1.6, we encouraged our SAML users to use Shibboleth, as it was the only SAML authentication option we offered. However, to better support their minor differences, we’ve added more fully tested SAML providers for v2.x: Ping Identity, Microsoft ADFS, and FreeIPA.