Many EVs already work this way. Mine has 6 "speeds" controlled by paddle shifters that create "engine braking" by changing the regenerative braking level. It

Many EVs already work this way. Mine has 6 "speeds" controlled by paddle shifters that create "engine braking" by changing the regenerative braking level. It is 100% a software/UI thing because if I press the brake pedal moderately it does the exact same thing, but continuously instead of in discrete steps.