if you watch closely, you will see he actually takes his hood off a lot but the show never puts him in spotlight in those times. like the one baseball episode. Kenny was in the little league, but you didn't see a parka did you?? he unusually hid behind stan the entire episode. so you see, you just have to keep your eyes peeled.
I do want to see Kenny with his good off and give lines that aren't muffled. His only actual line was in the movie years ago. But Kenny's one of my favorite character would be fun too so it'll be fun to see him like that.