Forbes and BusinessWeek are reporting that Longhorn will natively support RSS.
Honestly, I would be surprised if it didn't support RSS or ATOM at the OS level. RSS (et. al) is the “new HTML” and it's a natural course to see support it integrating into the OS just as HTML was in previous versions of Windows.
And just as in the late 90's when the browser became part of the OS, some people are not happy about the situation. Player-haters are as prevalent today as they were back in the day.
Check out this video on Channel9 demonstrating what Longhorn will do with RSS.