"Anything" is a big word.
Actually lots of people seem to want .doc, and certainly .pdf. But no one has ever asked for RTF before. That doesn't mean it's a bad idea. But it's the reason we don't have support for it yet.
To integrate RTF you'd have to write a media plugin. Take a look at the existing plugins in app/lib/core/Plugins/Media. The XMLDoc plugin is probably most relevant example. Your plugin must implement the IWLPlugMedia interface (app/lib/core/Plugins/IWLPlugMedia.php).
Since it will not be possible to generate preview icons for an RTF file you'll have to create default icons and put them in support/media_icons and then register them in app/conf/default_media_icons.conf. We are planning to replace the existing icons with nicer ones soon so definitely coordinate the design of the icon with us. Most likely we'll just create the icon for it ourselves so they are all uniform.
Last (but not least), your plugin should be able to verify that an RTF file is indeed RTF. Your plugin should NOT assume that any file it sees is valid RTF. If you do, you'll end up grabbing files in formats that are better handled by other plugins. The plugin will also need to extract metadata and text content from files it processes for search indexing. This all means that you will have to parse the RTF, make sure it is well formed and then convert it to plain-text for indexing.
Hope this makes sense to you!
seth
