I believe they will eventually. But first, the spec needs to be finalized (in progress), implemented in all the libraries that need to support it (some in progress, some unaware this is coming), and deployed by all federation managers and members worldwide (planning in progress). I'm excited for OpenID multilateral federation, but it's going to coexist alongside SAML for an excruciatingly long time. Probably not as long as IPv4 or Python 2, but the better part of a decade seems plausible.