It's an interesting point. Wth all the cries for them to release phone games I could imagine a PC game would make more sense. However, I think Nintendo would refuse to ever do it.
I could imagine scenarios where a pc game might make a lot of sense. Some big online multiplayer games (Such as Mobas or mmorpgs) might only be feasible for them if they release on both PC and Wii U with online cross play.
Here's an idea. If Nintendo ever created a subscription program, and created an MMO, they could release the MMO on both console and PC but require the full Nintendo subscription to play. Some PC MMO players might be use to paying $15 dollars a month for a new MMO but they'd now face the temptation of getting a Wii U for the other benefits of the subscription.
Will never happen.