In my opinion, there are two missing controls that would really make RadControls for Silverlight invaluable for sites that have user generated content:
1. Basic XHTML renderer
. User generated content is traditionally submitted and stored as XHTML, so being able to render a subset of XHTML would be very useful in silverlight. The subset would be similar to what is used by RadEditor in these support forums, plus possibly images as well.
Some proof of concept work has already been done here:
2. RadEditor for Silverlight.
Would be able to take user input that could then be rendered with the first control. It wouldn't need to be as powerful as RadEditor for ASP.NET - just supporting the basic subset of features that the XHTML renderer could handle. Being able to upload photos using RadUpload for embedding in user content would be awesome.
I'm obviously asking for personal reasons - my own site relies heavily on user generated content using RadEditor and RadUpload, and the above missing controls are all that is stopping me from writing a silverlight implementation - but adding these controls would enable a whole new category of silverlight websites.