I would like the ability to categorize my books (on PC if necessary) then have the ability to filter by category on the hardware.
The built-in wifi would also be infinitely more useful if it could access RSS feeds directly. If you could bookmark an RSS as a title, then when you access the title, it could fetch the latest update of that RSS feed.
I know calibre will do that for you, but that requires a daily sync. I see no reason the device couldn't fetch the RSS feed directly. Most of the necessary code is probably already in the firmware and used for access to newspapers, magazines and the shopping functions.