I've written what should be the final draft of the specification for the "feed" URI scheme. From the abstract

This document specifies the "feed" URI (Uniform Resource Identifier) scheme for identifying data feeds used for syndicating news or other content from an information source such as a weblog or news website. In practice, such data feeds will most likely be XML documents containing a series of news items representing updated information from a particular news source.

The primary change from the previous version was to incorporate feedback from Graham Parks about compliance with RFC 2396. The current grammar for the "feed" URI scheme is

feedURI = 'feed:' absoluteURI | 'feed://' hier_part

where absoluteURI and hier_part are defined in section 3 of RFC 2396. Support for one click subscription to syndication feeds via this URI scheme is supported in the following news aggregators;  SharpReader, RSS Bandit, NewsGator (in next release), NetNewsWire, Shrook, WinRSS and Vox Lite.

The next step will be to find somewhere more permanent to host the spec.