I wish I could remember where I read that bit and who, exactly, is involved. But, somebody has the same idea to use RSS as an ad feed, basically. The idea is to do exactly as you propose, to make shopping feeds based on categories. Not news feeds - product/site ad feeds.
Anyway, I think it's a great concept. It can certainly succeed, especially considering the all too common dissatisfaction with adsense. There is definitely a future in it, but I'm thinking the big boys will have it pretty well sown up.
Here's some links I just googled:
http://worcester.typepad.com/pc4medi...cial_rss_.html
http://rss.weblogsinc.com/2005/07/07...announcements/
http://channels.lockergnome.com/rss/...s/amazon.phtml
http://www.intel.com/intel/rss.htm
It's not a new concept. But, it hasn't taken off yet. There may well be an opportunity for a small-time company or individual to get a piece of the pie.