Replying to both your and parent post at once:
Using RSS for this seems reasonable for people who already have the ability to host a feed. I was thinking more about the Twitter-alikes for the "normies" who don't have a place to host a feed. I don't just want to see recommendations from bloggers. I'd like to be able to pull recommendations from a wider net of "content consumers" as well as "content creators".
I can't come up with an economic model that would work to run a hosting service for feedreader-generated feeds except in the case of for-profit feedreaders. There's abhorrent models there like, say, peppering the recommendation feeds with "sponsored content", or extracting demographic data from the participants and selling it. Making the recommendation feed a fee-based service also seems like a bad model, too.
That was why I look at the Twitter-alikes for the recommendation feeds-- because the transport is "free" (or, at least, not something where I'd have to worry about the business model).
