I think basically you want reddit's early marketing, "the front page of the web". Except it's your front page. It's a feed where you can go to see the latest stuff from everywhere you're interested in, rather than having to check each site individually. Like how one's reddit home page shows posts from all the different subreddits to which one is subscribed.
I think the best entry point is probably the browser, like Firefox's "top sites" on about:home. The browser is uniquely positioned to know what sites you frequent. If it also knows where to find those sites' rss feeds, it could automatically suggest adding them (also on the home page or similar). Once you've got that -- people actually using it -- you're over the hump, and it's easy enough to for users to transition to curating their feeds, using a different application, etc