I'd guess a Gamepad "Light". Smaller, lighter, more ergonomic and better looking. And with more battery life. I don't think we'll see anything else. Nintendo just released Wii Fit after a year's delay. Any other accessory probably will also be delayed a year, and they still have an uphill battle selling people on the original add-on, the Gamepad itself. Nintendo needs good ole fashioned software, and something that doesn't need anything extra to go with the Wii U.
As I said, I wouldn't buy the Nintendogs game if it happened but this is Nintendo. They were the add-on kings last gen, I expect something and pretty soon. Plus, maybe a Nintendogs U with haptic feedback could help sell the idea to the casual gamer?
Either way, I agree. I'm hoping they just continue to release amazing games and if the Wii U sells piss poor, no loss for me. I just want great games