Aww man. That's really disappointing. I mean, I'd still get the game even if there was no multiplayer and Link was the only playable character, but this certainly sucks. This would have been one game I'd have played a lot of online. Probably would have played more of this than I do of Mario Kart.
Edit: apparently some are saying there might still be PvP? That might honestly be even better, though I do still love me some co-op, and I don't see why they can have one but not the other. We'll see. Either way, day one purchase for me no matter what.