The job of judges (if they are doing what they are supposed to do) is to interpret the law as well as to determine if a particular law is constitutional. I've never read the text of the ADA so I have no educated opinion but, the question is, does the ADA, as passed, require the accommodations sought.
If the legislative intent was essentially to provide access in workplaces and in public for people who had mobility related disabilities, a theme park might not even be required to provide any kind of accommodation for autistic people to not have to stand in line. It doesn't really matter what the DOJ says or what rule might be put in place by a federal agency. They can be challenged in court to determine what kind of rulemaking the law allows.
Using my nephew as an example. He has pretty severe autism. If he waits in a long line he will very likely act out and cause a scene and very possibly start hitting whoever happens to be near him. Does that mean he doesn't have the ability to access SDD or 7DMT through the standby line. Technically he has access it will just be a miserable experience.
For somebody with IBS (which my mom has and I don't really need to hear about it), if a theme park has to provide a way to reduce wait times for the person so that they don't need to use the bathroom during the queue, does a movie theatre then need to provide a seat with a built in toilet in the auditorium so they have "access" to watch a 3 hour movie? I know that example is over the top but there are just things that people with certain conditions can't do. My mom won't go to a movie or a show anymore because of her condition. It sucks but it is what it is.