This is the reason for the Wii and DS servers shutting down as they were helmed by GameSpy.
Though honestly, Mario Kart Wii and Excitebots: Trick Racing are so much fun to play online, I wish Nintendo would set up their own in-house servers just for these two games, but it's not gonna happen. Both still have a good amount of people playing and I've been getting in as much playtime as I can before May 30th (Nintendo's cut-off date).
Maybe there'll be a Wii U sequel to the Wii Excite racers.