For the IdM side of things, there is SCIM: http://www.simplecloud.info/ It started as Simple Cloud Identity Management, but once it got to IETF, it was changed to "System for Cross-domain Identity Management". This initiative has been backed by Google, Ping Identity, Salesforce, Cisco, SailPoint, UnboundID, and others. You can see some of these names on one of the RFCs: http://tools.ietf.org/html/draft-ietf-scim-core…
Either is the standard, either it the the most adapted product/company (not necesseraly technologically) which wins the pot. This is technology AND business model, user community, strategic partnerships which will make an API to rule them all a defacto standard which will lead the programmable web. But you're right that IETF standards for APIs may be so long that I consider it is not possible untill decades !(or a leader which will open and free its winning standart to all only)