I've wanted Tumblr to allow you to subscribe to external rss feeds for a while (I think it did at one point) -- some of he blogs I read are text heavy, some are graphics heavy, etc., and it would be nice to have separate readers optimized for the different types of content. It would be nice to be able to subscribe to "tumblrs" on the tumblr dashboard whether or not they're actually hosted on tumblr.

Reddit's kind of the same thing: it would be nice to have a reader integrated with the discussion.