Nintendo will add the ability to patch software later this month, with Mario Kart 7 due to get an update in July.
Satoru Iwata revealed that Nintendo will release a patch to fix issues with shortcuts that cause problems with online play, though didn't specify which shortcuts would be affected. Previously Nintendo has said it has "no plans" to fix the Maka Wuhu glitch that renders the course virtually unplayable online, but let's hope it'll address that issue.
Other games to get patched will include New Love Plus and Kingdom Hearts 3D: Dream Drop Distance. You'll need to download the relevant patch from the eShop before starting play, just like with Virtual Console and 3DS Download Software games.