Timeline on a cross-site spec?

Our site [1] tries to provide a uniform XPath-based way of accessing data
transmitted via XHR. JSON and XML are prevalent but the lack of cross-site
support forces people into using workarounds (JSON in script, etc.) which
make things harder for us and probably everybody else also.

I'm sure you're aware of this and I'm just wondering on the timing of a
cross-site spec.

Mike

[1] http://www.webrpc.com