Tim Bray and Jonathan Borden have come up with a simpler version of RDDL as part of the W3C TAG's work in this area.

The proposal is very simple: just add two new attributes rddl:nature and rddl:purpose to the standard HTML <a> element. The nature is a reference to a URI describing the nature of the resource, e.g. a schema. The purpose is a label that describes what the resource is for, e.g. validation. (There's a full list of RDDL purposes here.)

Very cool work which is simple enough to address the main problem with current RDDL resources - maintainability.