I like the spirit of your proposal, though I'd like to utilize the contents of Eran's new XRDS-Simple spec once they're published (this will allow us to move to a single XRDS-Simple service type, and stay inline with XRDS-Simple as it evolves).
In any case, we probably want to have XRDS-Simple go final (or close to, at least for the parts we use) before we go final.
david