If you work at Nintendo, read this. I can tell you how to get multiplayer to work on 3DS VC and more

So basically, you release an update to the 3DS's OS which lets the 3DS send out a special signal when a VC game wants multiplayer. Other 3DSes can receive that signal, obviously. The multiplayer fun in Mario Kart and PAC-MAN begins. And you can connect with Game Boy (Advance)s via a special adapter distributed via Club Nintendo (yeah I know they already did one with the GB Pokemon remakes but not all titles support it and it's frequency isn't the same as the DS's). You can also distribute a Game Card for DS (Lite)s which lets the system send/receive the same signal.

Now, some of you may have used a Transfer Pak or Nintendo GameCube–Game Boy Advance link cable before. As far as the NGC-GBALC goes, you can do something similar to what you did to multiplayer: release a Game Card for DS (Lite)s which lets the system send/receive the special signal, include it in the 3DS software update and release a special cable via Club Nintendo. For the Transfer Pak, we're getting a bit more complicated. You release a software update to the Wii (U) that allows sending and receiving of a special signal which is used for N64 Virtual Console titles. Then you release some downloadable software for the 3DS where you can select a Game Boy game to stick in the Transfer Pak. Or, at least, pretend to. When you've chosen your game, you can send its data to the Wii (U) and then trade data. The traded data is then sent back to the 3DS.

If you work at Nintendo, please bring this up at the office. Thank you very much and have a nice day.