Maybe it's possible that there will be multiple Mario Kart installments for the 3DS? (Of course they could've made it Mario Kart 3DS 2, but that sounds kind of stupid, but then again Super Mario 3D Land sounds equally as stupid.)
Mario Kart 7 does sound weird, but how about this?
That portfolio of names sound even more weird than:
Super Mario Kart.
Mario Kart 64.
Mario Kart: Super Circuit.
Mario Kart: Double Dash!!.
Mario Kart DS.
Mario Kart Wii.
Mario Kart 7.
I mean, in the Windows family, they went number to name, and back to number, while Mario Kart used something random for the first 2 games, then they were using long names in the past generation, then they were using console names in the current generation, and now they seem to be using numbers in the next generation.