The simplest way to design an API, is to use an existing one. I work with a CMS where JSON documents are posted using the WebDAV protocol. Settings for documents and folders are all set with the PROPPATCH verb. The WebDAV protocol has defined API's for ACL, versioning and namespace management like delete, move, copy.
I really like the constraints you set on your project: "Build a CMS, no forms allowed". Aloha and other wysiwyg editors can hide the CMS almost totally. Using RDFa to store content is not a bad idea.
If you're interested in integrating VIE into that system, then the EU-funded IKS Project might be able to help you with that: http://www.iks-project.eu/get-involved
Info about Vortex CMS (in Norwegian): http://www.uio.no/tjenester/it/web/vortex/