I don't think it would have to be only electric cars, if you're building a hybrid where the 12V battery is kept charged by the high voltage battery, you've got basically the same situation.
Availability of accessories seems like it would be inconvenient for any early adopters, e.g. you can readily get USB chargers, portable generators, coolers, tire inflators, battery boosters, etc. that run off 12V... if you get a 48V vehicle today, you'd either need a 110V->12V adapter to run accessories, or you'd be limited to 48V RV accessories.
Availability of accessories seems like it would be inconvenient for any early adopters, e.g. you can readily get USB chargers, portable generators, coolers, tire inflators, battery boosters, etc. that run off 12V... if you get a 48V vehicle today, you'd either need a 110V->12V adapter to run accessories, or you'd be limited to 48V RV accessories.