I'd wager either a device which is essentially an add-on for iOS and Droid devices (not likely), or an iOS/Droid-compatible portable with some sort of dock in order to play at home, or possibly communicate with the WiiU in order to help boost interest in the console. Either way, the idea of bringing iOS/Droid games home, which isn't really a thing right now.
It seems almost a no-brained for Nintendo. This will allow them to test a physical media-less console with virtually no risk of damaging their 3DS brand, it gives them access to a whole slew of developers which the home console game companies have never tapped into before, and potentially access to marketplaces which are already VERY well established and reach the vast casual gamer market with virtually zero new infrastructure and/or marketing needed. While I don't think it's likely, an alliance with Apple seems like a win-win relationship. One which would help Apple get into the gaming market as a "serious" player, while letting Nintendo continue its quest to convince everyone on Earth that they're a gamer.
I see really little kids running around with $600 iPads all the time. I'm sure parents would jump at the chance to give them essentially the same thing in a more affordable, and likely far more durable package (I imagine it would be wifi only, no 3G/LTE support).
Nintendo doesn't do what everyone else does. If anyone seriously thinks that they're just gonna roll out some sort of PS4/XBO killer, then you've got another think coming. They no good and well that just another "me too" console won't matter in the least.