I think it can be dangerous if you don't get enough calories. Calories = energy = heat.
I looked into this because I started to eat more raw and higher fruit the other month at the beginning of winter and most people who eat this way say as long as they eat enough and maybe slightly increasing their calories the colder it gets, they feel fine.
This fruitarian gal started a channel specifically for 80-10-10 in the winter time:
I don't know what to think yet about the theory that fruits are too yin and not suitable for cold weather. I haven't seen any fruitarians that ate enough say they had to stop because they started feeling too yin around winter time. It's usually they have a hard time finding enough quality fruit during winter.