Nintendo's content should be the best obviously, but essentially make it as much of an MMO as it can while still being true to Mario Kart. I.e it need not be dependent on internet, but have a large online nonetheless. Like that I would expect MK8 to be a super killer app.
In this day and age, with the Internet, ignorance is a choice! And they're still choosing Ignorance! - Dr. Filthy Frank