But from business standpoint why waste money to make it possible to play games on other system when you can simply sell that other console for people?
Ideally, if properly marketed, 3DS Player is what gets people excited (thanks to the overwhelmingly good game library) to buy a cheaper Nintendo home console alongside a PS4 / Xbox One, which in turn due to being bundled with a Wii U GamePad gets people interested in the Wii U itself ("Like what you see? Then imagine playing in HD!"), which in turn helps Wii U sales.
This assumes several conditions:
1) Nintendo acknowledges Wii U hardware sales are bad and wants to try the same (failed) approach again as with the GameBoy Player for GameCube
2) Nintendo wants customers to see the Wii U as an upgrade from the 3DS, even though current marketing suggests the opposite
3) Nintendo isn't afraid of having its own products cannibalize each other (e.g. like Apple)
4) Nintendo is willing to make a Wii U bundle WITHOUT the GamePad to provide an upgrade path for the "3DS Player"
We've already seen some things happen:
1) DS Virtual Console games are coming, so the idea of having 3DS games on a TV is not far off should DS VC succeed
2) Nintendo Network ID will become unified for both 3DS and Wii U, tying purchases to an account vs. device
3) Games are starting to have more connectivity options between 3DS and Wii U (e.g. use 3DS as controller in SSB for Wii U)
4) New 3DS is taking off with strong developer interest, now is the time to squeeze every last profit out of the 3DS brand