1. Media transcoding and resizing, at source level
The source (ie. the site that sends out the feeds) should prepare mobile-optimized media format -- otherwise the enclosed media may not play well on mobile devices.
In the web/PC world, various media file formats are used and most devices can play them well -- WMV, MPEG 4, AVI, FLV, DIVx, you name them. But often on mobile devices some file formats are not supported. Also there might be file size issues: most mobile devices will struggle with a 30MB podcast.
There can be a middleware doing the media transcoding and resizing on the fly, but it would consume a lot of server resources and may not guarantee a realtime media conversion. Any amount of time lag will annoy the users.
Therefore the best solution would be for the source sites to prepare mobile optimized media files and include them in their feeds.
2. Full text feed
Some sites only include excerpt in their feeds, hoping the user will click to see more content, thereby increasing the site traffic.
Presumably this practice stems from the fact feeds don't have a solid advertising model as websites do -- hopefully companies like will solve this problem.
But mobile users, with more limited screen space, will be more hesitant than web users to open a new browser window and visit the original site, and then come back to the feed reader to view the next feed item. Therefore the importance of "full text feeds" is greater in the mobile environment.
3. Selective download of content (text / media)
With many mobile users still not have adopted unlimited data plans, users have certain anxiety about accidently downloading huge media files over the air, costing them lots of money.
Therefore, the mobile RSS service provider can think of a hybrid model, where text content gets downloaded over the air, while the user can "turn off" downloading of media files over a certain size.