I don't believe there are any current plans for additional content beyond what is available in the selected RSS feeds. I'd be surprised if that doesn't include some popular newspapers and magazines, but I haven't seen the initial list.
There's always the possibility that someone will code something to make it easy to transfer over your favorite content snipped from the web and RSS feeds. Something like a new version of Sunrise is what I'm really hoping for. (
https://www.mobileread.com/forums/showthread.php?t=2815)
Plus, there's always the possibility that something else is in the works that Sony isn't able to talk about yet.