Pretty much no vehicles currently do #3, despite many being capable of it with software-only changes.
I believe this is because most vehicles do a fixed amount of regen(which goes into the battery) when the foot is off the accelerator, but no additional electric braking when the brake pedal is used. I think that's because current regulations have pretty much stopped modifications to the braking system in cars, and prevent tweaking it to do electric braking when available to do cabin heating, and mechanical braking otherwise.
With a seat heater. They were popular in the old times, when engines were not digitally controlled and took a long time to heat up enough to provide any warming effect inside the car.
Every car I've been in in Norway has had heaters in at least the front seats. The Tesla S has rear seat heaters as a configuration option when you buy the car as well as an option for a heated steering wheel. Quite a lot of the cars I rented in the US had heated seats, even in North Carolina.
Recommendation #2: pre-heat the cabin
Recommendation #3: if/when driving in stop&go traffic, use the regen energy directly for heating to save some charge/discharge cycles.
Recommendation #4: along with #2, use some phase change materials to “charge” some thermal batteries.
#1&2 are a thing. Not sure about 3 and 4.
3 may require some predictive modelling to know if you’ll be driving in stop&go or not.