How accessible is the Great Wall for people with mobility issues?

Well, I just know the case of Badaling section. As I know, this section has already been equipped with barrier-free access, wheelchair lifts, and blind tracks to help those who have mobility issues.

There are no elevators. Cable cars are situated at a number of sites, though there are sometimes a flight of steps to get up to or out of the stations. The Wall is challenging for anyone with mobility issues and not really suitable for anyone with any serious disability. Search for some images to get an idea of different places. Mutiny has a reasonably sized platform at the top of the cable car from where the Wall can be viewed if you don't wish to walk far on the wall itself. There are some steps as well, though.