Hmm, this reminds me of the GTA naming structure. A number means it's the new, super-huge GTA sequel, a city name means it's pretty huge, and set in a new location, and stories means it's some half-hearted attempt to cash in on the popularity of the series. But I digress...
I'd say that, after SMG (Super Mario Galaxy, or submachine gun), Nintendo will likely start a new Mario theme. Or maybe they'll just make Super Mario Time...Portal...Thing. Hey, a Mario game with time travel would be cool...