We should add query parameters onto RSS requests, and gradually upgrade while remaining backwards compatible. Create clients and server features that are compelling enough, and people will update their server code.
That's a bad idea if you cache RSS in an xml file, i.e /rss.xml. It would make it more complex if you had to handle query parameters. The parser should just check for the version attribute on the rss node; <rss version="2.0">. Or, even better, it could just check for the availability of server nodes such as "<cloud>".
Or did you mean something completely different?