Some vehicles repurpose shift paddles as a way to trigger regen braking. But they're pretty gimmicky and not really useful for driving. If you want to use regen in a vehicle that supports it, the brake pedal does that. And when regen is not enough, the hydraulic brakes are also used. But a "sometimes brake" pedal that only support regen sounds like a bad idea. Vehicle controls as essential as braking need to be consistant in how they respond to input behavior.