Danges, with iOS, Android, and Windows RT, I agree with you. With some full Windows 8 Pro tablets, you basically get fully capable Ultrabook style hardware. Add in a Bluetooth mouse, keyboard (my Windows 8 pro tablet comes with a keyboard/stand) and an micro HDMI/VGA cable and you've got a machine that is every bit as functional as an ultrabook, but with the ability to seamlessly switch to tablet form factor and be used for media consumption.
When it all comes down to it, you may as well just keep your ultrabook and get a cheap Android tablet for media consumption, but you may also find that the types of tablets you are looking for are already here. I am really sold on my Iconia W700.