Well, that gets back to my comparison to Sony realizing that the PS4 was healthy and the PSV wasn't, so they axed the PSV and threw full support behind PS4.
Nintendo is doing the opposite. The 3DS is the most successful dedicated video system on the market at 60 million units to the PS4's ~42 million, and while the PS4 will eventually overtake it, it's unclear whether the XBox1 even by the end of its lifespan will touch the 3DS. The Wii U, by comparison, has been a disaster.
Why bank on a successor to the Wii U when you can bank on a successor to the 3DS, a system that is still selling large amounts of software despite being absolutely archaic? The NX is going to be the largest jump over the 3DS in system generational jump history...its GPU is going to be something like 100x stronger than the 3DS' and, given the 3DS' ridiculously weak CPU, that measure is probably even more ridiculous. Nintendo's portable is going to go from a 240p system that struggles to match the PS2 (with, admittedly, far more RAM than the PS2), to a 720p system that more than doubles the PS3 (with far more RAM than the PS3).
This strategy makes a ton of sense and is probably the only successful route Nintendo could take. The DS was indisputably its most successful system of all time (as much as people ignore it when they talk about the "Wii Era," the DS was even more important). Just as the DS pioneered a lot of stuff that cell phones later took advantage of, Nintendo could take advantage of the current widespread proliferation of tablets to market a larger, non-pocket-based handheld and stuff some actual computing power into it. I don't see why a Nintendo tablet with compelling software couldn't reach wide market proliferation, presumably with software like Cooking Mama and Nintendogs revived to help push it as a "more than a gaming tablet" into more conventional households.
Several of Nintendo's best titles ever are things like Brain Age and Nintendogs which don't even really qualify as video games. Brain Age is one of my favorite titles anyone has ever put out and, as much as people on NeoGAF sneer at it, I think it and Nintendogs have serious potential as fronts in Nintendo's push back towards the mainstream. Enough time has passed that people can be persuaded by a nostalgia push towards them.