In the recent heated debates about Echo (I'll call it that for now) the prevailing comment is that Echo is a replacement of RSS because of political issues. While this is not entirely untrue, there are actually big differences between Echo and RSS. I'm going to address the main difference for each version of RSS.

1. Why Echo is different from RSS 1.0 Echo is XML. RSS 1.0 is RDF.
2. Why Echo is different from RSS 0.91 RSS 0.91 is designed as a site summary. There is an item for each page on your site with a link and a title and maybe a description. This is the way the BBC and Microsoft use RSS. Echo is for distributing/transmitting content. Each entry contains things like author, an id, a permalink (if it is already published online), the relevant dates, and the actual content. This can be a weblog entry, or a comment or what else.
3. Why Echo is different from RSS 2.0 RSS 2.0 is XML, but Echo is really about XML technology. The only thing that is asked more than once on the RSS2-Support list, I think, is: Where can I find the XML Schema or DTD for RSS 2.0? There is no schema because it cannot be done. That's the backwards compatability burdon RSS is carrying. Echo will probably have a W3C XML Schema and a RelaxNG schema. The dates will be in xs:dateTime format, so languages with schema support (f.e. .net languages, XQuery, XSLT 2.0) can perform date/time calculations directly. Also the preferred format of the content seems going to be XML, where RSS 2.0 uses escaped HTML.

These differences are IMHO big enough to warrant a new format, and Echo deserves a fair chance.