I have 2 with DMD..I agree mobilitiy shouldn't be what motivates when you do the wish. My oldest did his when he was 12. He was using a scooter then but he knew who he was and what his passions were by then. He is now 15. His wish was to go to Normandy, France and see the beaches of D-Day and the American Cemetery. He wanted to honor those who fought in that battle and WW2.. He was diagnosed at 4. When he was little, he started a passion for all the planes of WW2 and we would go to the Air Museum here in Tucson quite a bit and he got to talk to the volunteers of which many were vets. Since he couldn't do sports he impressed his friends by all his war knowledge, airplanes etc. His wish was granted and we had a trip of a lifetime..A trip that was extremely meaningful to him and his interests.
We are now working on my 2nd son's wish. He is 11..He wants to meet the creator of Family Guy and be a character in an episode as he has decided he wants to create cartoons etc. We don't know yet if they will grant it but that follows his interests as well..just my thoughts and experience with it.