Is it really that impractical to put the motor in the car? The elevator anyway needs rails on the side, if for nothing else to provide something for the emergency brakes.
Use regenerative braking on the way down so you don't need a counter weight - although that does mean you need a much large motor, you might save on energy, but power requirements would still be high.
Assuming that the weights of the lift car and the passenger load
remain about the same, moving the motor to the car saves the weight
of the cable, but adds the motor, power contacts, and whatever
traction device (cog?) moves the car.
Adding regenerative braking adds some form of energy storage -
batteries, flywheel, compressed air, or whatever. A flywheel might
be lighter than batteries, but torque I/O might affect passenger comfort.
It would be interesting to see how CF holds up over time. ISTR that
Kevlar rope is very strong, but turned out to have unexpected issues
with repeated jerky load/unload cycles. Presumably the CF elevator
cable would have adequate testing before commercial use.
Use regenerative braking on the way down so you don't need a counter weight - although that does mean you need a much large motor, you might save on energy, but power requirements would still be high.