Funnily enough, I had a weird idea before for a dual screen hybrid console. As a handheld, it would be like a DS. To dock it, you can take the screens apart, dock the top screen, then use the bottom screen as the controller, like a Wii U. I thought this was a dumb idea and that Nintendo would never want to repeat the Wii U, but... Hey, who knows?
I don’t think the Wii U’s issue was that a controller was a screen; I think the Wii U’s issue was that everyone thought it was an add-on for the Wii and wondered why it cost more than the Wii itself did
My issue with the Wii U was that it was almost, but not entirely, portable. For some games, you could play entirely on the tablet, without the TV even being on, as long as you stayed relatively close to the TV. The issue was that you would start getting lag spikes when you tried to push the range and not enough games supported playing entirely on the tablet.
I would not object to a console that is whole house portable (probably via LAN, like the PlayStation Portal). I almost never play outside of my house and when I do, it is always at a location where I can connect a box to the network, like a friend's home or a vacation rental.