A service like PS+ sounds cool, but others have mentioned the inherent problems when trying to pair it with Nintendo. I think the current Club Nintendo rewards + Nintendo Network Premium service are pretty good for now, but if they really want to hit it out of the park:
1) Give Nintendo Club coins for third party games too! I believe this is a small but noteworthy reason why Nintendo games outperform third party games on the same console. When a buyer is standing in front of a games rack, he or she should be thinking, "But if I get it for the 3DS or Wii U, I also get free, spectacular swag!" instead of "Why would I get the gimped Wii U version?".
2) Make the Nintendo Network Promotion a permanent thing. I've probably bought more things from the Wii U eShop already than I ever did on Wii. Make it a more prominent part of your marketing to get people in the eShop and looking at your wares, and more willing to spend cash. That free credit goes a long way.







