Nintendo president Satoru Iwata has stated that the gaming giant only plans to bring one New Super Mario Bros title for every Nintendo platform. He also admitted that it has been quite a challenge to bring two games of the same series, New Super Mario Bros 2 for 3DS and New Super Mario Bros U for Wii U, in such a short amount of time.
“We only create a New Super Mario Bros. title one per platform,” Iwata said, while acknowledging that is unusual and a “challenge” for the company to be making two for the same calendar year, one for 3DS and one for Wii U. “I think we’ll probably go ahead and continue at that pace. That being said, that’s probably [Mario creator Shigeru] Miyamoto’s choice, so I can’t give you a 100% guarantee that that’s the pace we’ll continue at.”

I honestly think they need to tone it down a bit with Mario. Plenty of other series that could do with some attention.