This isn't too exciting from the outside looking in. It's kinda how in Super Mario Galaxy you could have a second player use a wiimote to grab star bits.
Heh, we knew this months ago! But it's awesome to say the least. I hope all Nintendo first-party games (well besides Zelda, haha) have co-op support in some way.
The Switch is a walking engagement machine and co-op experiences cement new players into the ecosystem; once you try it, you'll probably buy it!