Are you talking about the charging circuitry?
What are the requirements for the motor(s)?
Motors, for instantaneous current, can easily exceed 100kW, some much much more than that.
Even assuming limitations to 100kW (which, would be very low for motor current), that's still 2000 amps at 48V. Remember, 100kW is ~134 hp.
Also, the problem is definitely also the cables in your car. Moving to 48V would mean amperage would increase by 10-20x, which would mean cabling thickness would have to increase substantially.