I *REALLY* hope Plex includes server-based TV tuner/DVR support. (i.e. Set up a Mac mini with a TV tuner to act as recorder.) I'd love it if the new AppleTV could be my single interface for all big-screen viewing.
There is a way to watch recorded tv shows in plex, I use an eye tv with my Mac mini and created a new channel called eye tv and pointed it to the location the eye tv app saves it's recording, works pretty well