Yeah, this has been discussed on and off since Ouya first made its vapourware appearance last spring. Mostly in IRC, although someone did bring up Ouya in the discussion here: http://hedgewars.org/node/3248

Android multiplayer already exists since this summer, although not on the marketplace since the dev who did it didn't have key access. Poke Xeli to see what's going on with that. He hasn't been around for a while.

Higher res graphics isn't going to happen w/o new graphic artists. More fundamentally, there's the issue that most hats are community made, and low res hats on high res everything else would look odd.
But, I think you are maybe possibly misunderstanding HD TV. HD TV is *not* higher res than a computer monitor. 1080p is basically a 1920x1080 monitor. That's the resolution of my computer monitor, and hedgewars looks fine on it. For one thing, the default resolution is zoomed out to ½ so pixelation isn't really visible.
Now, of course HD TVs are a lot larger, but on the other hand, I sit closer to my computer monitor than people do to a TV, since if you sat less than a metre away from a large-screen HD TV, you wouldn't be able to easily see this whole screen. As a result, the visibility of pixels is still about the same as on a computer monitor.
This is similar to the "retina" claim by Apple, where the pixel density on the iphone was significantly higher than on the ipad, simply because people hold the phone closer than the tablet.

I doubt very much an on-screen keyboard would be added to the engine. That seems more suited to the console itself, as an overlay, if possible. Reimplementing a keyboard in any game that might have chat because your console has no functionality for it sounds really impractical. Better to use a hardware keyboard, or, yeah, some console generic overlay.

Chance is the device will allow for USB and bluetooth keyboards other than the onscreen "built in" android keyboard, so chatting wont be an issue.

The only thing that truly doesn't exist at all for android, is a controller focused 1920x1080 optimized frontend.

Hedgewars for Ouya would be pretty cool and porting it wouldn't be hard since we've already got an Android port.

Looks like my ouya will arrive soon. I can help you with testing or whatever...
I was an active player a couple of years ago, but not now. Still I want to help to the project

Might as well add the "Game Stick" to the suggestion pot, as it should be around the same thing as the "Ouya" in the end.