Oh, I thought this would be more of a Construct thing to announce as a feature, rather than be tied up by Nintendo. After all, all someone has to do is release a trailer for their game made with Construct 2 which shows both screens working independently and we'll all know the answer.
In the meantime, having your hands tied means you have potentially less features to announce for Construct 2. I don't see how anyone wins regarding keeping this a secret... apart from Nintendo if their plugin only supports the gamepad, and they don't want people to find that out until it's too late... but I doubt that.
In any case, I guess I'll play the waiting game until I see more, or get my own license, but I doubt I can start planning any Wii U games until I know the answer, as it's pretty integral.