In cold weather, make the car more efficient and perform consistently by using regen power more efficiently.
In cold weather (eg: less than about 40F, 5C), the battery can’t accept the high currents of normal regen. Currently, this is addressed by making regen weaker depending on the battery temperature. This makes the regen-braking force inconsistent and makes me use my brakes more (wasted energy).
When using regen braking, the power could optionally be used to heat the cabin. Any power beyond the heating capability (limited by the power of the heater or suitable temperature deviation from the user-set temperature) could be used to charge the battery. If there is still power beyond that, it could go towards heating the battery up to temperature. If all those uses are exceeded, only then would regen be limited.
Full-regen is about 70-50 kW. The heater is about 4-6 kW, and the battery heater (ie motor-heating) is about 4-6 kW (only in the S/X, no battery heater in the 3) (note that while there is technically no actual battery heater for the 3, they send specially designed, inefficient pulses of power to the motor to heat the motor which is thermally connected to the battery; this is thus the equivalent of a ~4KW heater). This may be only an incremental improvement but may increase range slightly, make the battery more efficient, and make regen more consistent.
Moderator: Extending this idea a bit further, seats without passengers could have the seat heaters turned briefly on during deacceleration to consume a bit more power.
While not every secondary idea is implemented, the primary request for better cold regen has been Implemented in all Tesla cars with the heat pump (S/X/3/Y) and improved battery technology.