Here's a question--could the Atom API be packaged as an extension to RSS? I'd have to read the spec to see where the mismatches might be, but I would think that at least a subset of the API could be made to work with RSS. That way, a site that has standardized on RSS as its publishing format (for now at least) could begin to take advantage of the benefits of the API. The site could also publish feeds in both formats.

One might think that there'd be no point in doing this--if you want the Atom API, take the Atom format too. But there would be benefits for existing RSS clients being extended to support the API for working with both the Atom format and RSS: First of all, the Atom spec is still incomplete (both on the API and format sides). So there is something to be said for using the new API features with a more stable file format. Second, some feeds may not need, or even be able to provide, all of the elements required by the Atom format spec, so RSS may be preferable.

Finally, the fact that the Atom spec is divided into a file format spec and an API spec makes this kind of thing natural. Why do it? Why not?