I don't mind the size at all, I have to take my Wii U with me regularly if I want to play with friends and a somewhat portable system with a dock sounds kind of perfect for that. Even more so, if I could buy a second dock...
720p sounds kinda hard to do, if you want to get good running times with graphics, that are better than the Wii U. But we don't know how energy efficient this thing is build, so maybe it is possible to get more screen time out of this than the 3DS.
720p would also be the least, I expect from Nintendo when it comes to the docked version. It seems like 540p would have been better to enable an easier rerendering for 1080p, but if they offer 60fps 720p for every game on the system and if it's also prized accordingly (!!!), I'd be okay with that.
I'm looking forward to the reveal. As long as this thing supports great local multiplayer sessions without the need for a sideways wiimote (hated what the small the d-pad / no analog option did to many games) - I'm game. I'll be there day one. Mostly likely I'll be there day one regardless, but this is the one thing I'm a bit anxious about.
I'm already sure that Nintendo will deliver on the games side and they got amazing results out of the Wii U hardware, so I don't care too much about that.
But they fumbled a bit, when it came to local MP this and last gen. Not in the amount of games, but in the implementation.