Interesting post, on another site, from a Leaf owner.
Battery packs that need to be heated - already do this automatically. For our 2015 Leaf, it is most important to heat the battery during charging - and it does this.
I actually don't mind wearing a coat and gloves (and hat if needed) inside the car - because that is how you have to dress to be outside in cold weather. You're out of the wind, and heated seats are quite nice, and they take virtually nothing away from range.
Heating the battery, though, does become noticeable when it gets really cold. Low teens* and below, the range is affected.
The ONLY time you need to use the heater - is to keep the windows clear, or to melt ice.
* 13°F is -10°C.