Below is a list of proposals people or companies have made for RSS. Non of these are widely adopted standards. (So don't expect any software to support them.) But some of them could become standards in the future.
NOTE: Those in the list below that are marked "In Development" should NOT be implemented. "In Development" means that they are still working on it and trying to come up with a draft. Those labeled with "Draft Exists" can be implemented, but be warned that they could radically change.
|Easy News Topics||Easy News Topics (ENT) is intended to be a very simple standard for describing how topic information can be introduced into an RSS2.0 news feed.||Draft Exists|
|ICBM||Let's you add latitude and longitude info to an item.||Spec Exists|
|iTunes RSS||iTunes Extension Modules used for IPradio/podcasting.||Spec Exists|
|Media RSS||RSS Extension Module used for IPTV and IPradio/podcasting.||Spec Exists|
|Newsgator Feed Extension||Created to make RSS feeds work better with Newsgator software. Lets you specify an image, up to 277x78 pixels. And lets you specifies a specific rendering transform (XSLT) to be used when rendering the feed in NewsGator for Outlook. The transform must already exist on the machine running NewsGator; stylesheets will not be downloaded or installed automatically.||Spec Exists|
|RSS Disposition Hinting||A proposal to make it so IPTV and IPradio/podcasting works better with RSS. Uses an HTTP "Content-Type" parameter to hint at an RSS feeds disposition type -- to hint at what is being syndicated.||In Development|
|rssHints||A module that adds elements to a feed that help an aggregator process them.||Draft Exists|
|Source GUID||When an RSS item is posted in response to a previous item (called the source item) RSS 2.0 offers the source element which allows the item to refer to the RSS feed which contains the source item. The SGUID specification provides a more granular approach by offering an sourceRef element which can reference the GUID permalink of the source.||Draft Exists|