GeoRSS is an open (as in speech) and evolving standard. Anyone is free to submit proposals for extensions or modifications of the standard.
To submit a proposal, first create an account and login. Then create a new page stating your proposal, its intended use and example use case, and some example format snippets.
After an initial discussion period the proposal will go up for vote by all members of the GeoRSS community. If the proposal passes by a simple majority then the proposed modification will be adopted into the next version of GeoRSS.