Boxee also did a great job of combining sources and did a good job with local storage. It also didn't support DVR.
To be honest DVR is an animal that I've seen nobody crack successfully.
Also, most (all?) Roku's support local storage, but it isn't ideal. Usually, I need to throw some content on a thumbdrive and stick it into the Roku. Not horrible, but I wish I could use the Roku to download content to use it to stream via DLNA.
Also, when I last tried to use Plex (though, this was more than a year ago), it was extremely clunky. Maybe things are different now, or maybe I was expecting it to behave differently, but I didnt like it.
In fact the very reason I switched away from Boxee and Moovida back to vanilla XBMC was because I wanted a media player that separated my music and videos and respected my file system hierarchy.
However looking at the screenshots for this project, it looks like it separates music and video in the same way XBMC does. So I'm not really sure I understand your point.
What you're describing isn't really a feature I personally want (just having random YouTube results mixed in with offline content would annoy me), however I can totally understand why it would be preferable for many other people.
> Furthermore, a good application would keep tabs on release date and watched status for me, like you'd expect from a DVR.
To be fair, XBMC does do that.
Have a DVR-like interface, where all content is combined. This means downloaded torrents (by new and/or watched), with meta info. Also include new streams from HuluFlix based on when they were made available. New shows recorded from antenna and maybe QAM. New movies from Crackle, etc. The point is, I should be able to tell the application that I want all new episodes of "The Simpsons" and it will use all available configured sources to find what I want. It will present this to me in one comprehensive list. The source is irrelevant and I don't want to start various apps to find what I want. Google TV sort of tried to do this and failed. As cool as XBMC and their ilk are, they suffer from not passing the "wife test" and feature bloat. This thing, in my mind, should be dead simple to use.