"Then the challenge of clearing roads of EVs with flat batteries. Not quite as simple as a few jerry cans of fuel and some jump starts."
Unless somebody started their journey with a minimum charge, draining the battery and having to be towed from the motorway isn't going to be an issue. Most EVs have heated seats that don't take a tremendous amount of power. You also aren't sitting in the car with an idling petrol/diesel engine. If we take 60kWh as a modern average EV battery capacity and it's at 50% charge, then overestimate the seat heater power at 1kW (or 500W x two people in the car), that's still 30 hours before the battery is completely flat. Very slim chances of so much snow that it's 30 hours for crews to clear a lane to get vehicles off of the motorway and someplace where people can hole up in a hotel, restaurant, etc.
It's far more likely that people will have far more of a charge in their battery anyway and the seat heaters aren't so power hungry.