What could be some teachings that Buddha has not revealed to us?

In Maha-parinibbana Sutta Buddha has said: > "there is nothing, Ananda, with regard to the teachings that the > Tathagata holds to the last with the closed fist of a teacher who > keeps some things back." however, in Simsapa Sutta Buddha says: > "there are many more things that I have found out, but not revealed to > you. What I have revealed to you is only a little." Do we have any knowledge about the teaching that he has not revealed to us? The commentary on accesstoinsight writes, "This famous saying has been taken to justify the doctrines of various Mahaayaana schools, Theosophy and so on." Could that be the teaching of tantra? I hope there's some good insight here.