A hybrid is bad IMO for a few reasons:
1. Revenue is contained to only one unit.
2. If it fails they'd be in big trouble.
3. Would it function more as a console or portable? If its underpowered then devs won't want to work on it. But at the same time many publishers like the fact that portable games are cheaper to work on over HD titles, and a lot of titles wouldn't be made if that wasn't an option. This seems lose-lose.
It's much safer to keep consoles and portables, and make both enticing.
Also, what they SHOULD do is to continue to allow their consoles to stream portably like with the Gamepad, AND give you a TV out option for handhelds.