You said thatyou have had him checked out at the doctors. Did this rule out things like Asperger's etc. Very often children with ASD's have problems with food, sometimes texture, sometimes even colour. A child may only eat foods of a similar texture, colour etc. As long as he is getting all the nourishmnent he needs from the foods he eats then don't worry. I think it is a blessing that he will not eat anything in McD's anyway. Best to keep away from junk food places like that.
My son has Asperger's and he was admitted for assessment and an exclusion diet [ he also has ADHD]After 3 days of starving apart from eating cereal for breakfast they decided that he could have cereal for every meal if that was all he would take. Now he is nearly 20 and eats a far more varied diet. Just keep trying him with different things. Try to keep to the textures he likes if you can.

I knew a child like this. He was in my preschool class. He only ate dry foods, like cereal, crackers, croutons,etc.. He grew out of it. I think sometimes it's a control issue. As parents we decide everything for them. When to wake up, when to eat, when to sleep and the list goes on and on. One thing you can't control though, is what they eat. Let him have control of this for a while and don't make a big deal about it or give any extra attention because of it. He will give it up!!