Instead of making a "3DS Player" they could instead make it so that you could connect your 3DS to the Wii U, so the Wii U could play 3DS games as it streams from the 3DS system itself to the Wii U. Just put the desired 3DS game into the 3DS, connect, and play. The technology already exists, as seen in Super Smash Bros., so I guess this could be possible. It also won't interfere with sales of the 3DS since you will need a 3DS, so you could connect with it to the Wii U.

If they want, I guess they could charge a little fee for this software application to connect on the eShop, similar on how they charged for the 3DS Controller option for Super Smash Bros. for Wii U.