I can see Kei cars being successful in North America.
More people are getting conscious about gas mileage, and kei cars are CHEAP. They can be bought from $7,500-$8,000 range.
Sure, you can argue they're slow and ugly, however Smart car was not exactly a good looking/fast car either.
Also kei cars can carry more people, luggage, get better gas mileage than smart car too.
Daihatsu Cocoa
Honda N Box
Daihatsu Move
Toyota Pixis
Mazda AZ-Offroad
Subaru Stella
Honda N One
Mitsubishi Minicab Camper
Nissan Moco
Mazda Flair