I haven't seen anyone posting about this, so I'm sharing in case anyone else ends up with this problem. I purchased a 2018 S model with the all-weather package 3 weeks ago. During checkout at the dealership, I confirmed the heated seats and figured that was enough - too hot for the steering wheel to be necessary yet (but my wife will need it in the fall/winter). Last week, I got curious and decided to check out the steering wheel heater, but I had to check the manual to understand that the button is simply missing!
I called up the dealership and it took a while to get through to them that I DO have heated seats, so it's not just an All-weather-package missing kind of thing. The service department doesn't want to touch it because they don't have any experience messing with those buttons and harnesses, so they send me to sales. Sales says that there's nothing they can do because it's a factory installed option, and Nissan tells me to file a dealership complaint!!
As odd as it feels to say, I'm on the dealership's side on this one - there's nothing they could have done. I'll post updates as it develops. I haven't identified if it's just the button that's missing, if the harness is missing too, or if the steering wheel is missing the heater as well. I'm going to try to get a refund on the whole AWP, because warming my wife's fingers was the whole point of getting the AWP, and I don't see an aftermarket installation being worth the effort.
In the meantime, I've consoled myself in the knowledge that this makes my LEAF a potentially one-of-a-kind configuration!