At a recent investor meeting Nintendo revealed that they will be giving away a free 3D version of NES classic Excitebike. The game will be bundled with an upcoming the 3DS eShop firmware update that is coming in late May.
Unfortunately this offer has only been confirmed for Japan, so Americans and Europeans may be disappointed.
The fact that Nintendo are bringing Excitebike to the 3DS probably means that other NES games will be getting a similar treatment. If Nintendo keep this up we may have to rename the 3DS the FreeDS.