To be honest, Chiellini natural position was a left-back. He was brought in as a sub for zambrotta in early 2000. I think having him as a left-back will make our backline extremely strong. reason being, he is physically very strong and a great header. most of the wingers are very bad at heading/jumping. With chiellini marking them. They would have absolutely no chance of winning/receiving any aerial ball. Most of the fullbacks are often bad jumper/header, we are very lucky to have chiellini as a fullback
besides, i think he is more suited for fullback as he is full of stamina and grit. plus the fact that he loose concentration sometimes, which is more dangerous if he is a CB.