Yes, great idea, because all people who buy a smartphone or a tablet use it to extensively play games! Even better, let's drain those machines with little storage (I take my MP3 collection with me, so every size of storage is too small) of even more storage! YES, let's slurp more battery life from that already crazy powerhungry and low battery time device. Absolutely, Let's sacrifice physical controls supported by touch and motion for smearing our screens with imprecise no real feedback controls. Pure genius! Finally let's jump on that bandwagon where no game developer has ever sustained sales for longer times or where any single hardware seller has ever had a consistent hardware offering for longer than 1 or 2 years. Let's just hop on, on the pure believes that it will sell for the amount of money that's needed because....they say so...
[end of sarcasm]
The ONLY thing I'd ever see Nintendo do is a VC with very, very old games where if you buy it on your portable/home console you'll get it for free or a minor fee on your phone/tablet.
Microsoft is losing money on XBOX like a basket losing water. Sony as a whole is kept adrift by the PS related income. And Nintendo....well is Nintendo and operates like any other company in any other segment doing it's thing and being profitable most of the time. They take pride in what they do and will continue doing so as long as they are alive and can do this. The way THEY want to.