This may be an unpopular opinion, but I think Disney just may actually know what it's doing with these changes.
The varied and particularized needs by disabled persons visiting a large theme park are difficult to accommodate within the bounds of the ADA unless a program gives out an accommodation that fits everyone, like DAS. But DAS is unworkable because it's too close to Genie+, which is in itself a valuable service, leading to abuse at worst and overuse at best. And the DOJ advises businesses not to inquire into the nature and extent of a disability (in some cases, like service dogs, DOJ regulations actually prohibit all but two questions).
The DOJ regulations do not cover line-skip accommodations (skipping the physical line, not the wait), leaving Disney open to the broader "spirit" of the ADA, which is inclusivity as much as possible. So - unlike accessible seating or parking - no impact studies have been done and no guidance is given to the business as to how much negative impact is considered reasonable.
Court cases deal with particular plaintiffs, and a plaintiff suing Disney on the basis that their particular physical disability cannot be accommodated with line accommodations will need evidence in the form of medical expert testimony as to why that is true. Disney will also present experts. Look at what was said by the court in A.L. when he advanced all the reasons DAS would not work for him. The court considered all of the other things he could do and the advance preparations he could have made to deal with his disability in navigating the parks. The court did not concede to his choice, nor did it place all the burden on the business.
RTQ is going to be difficult for Disney for the reasons stated in this thread. But having a medical expert at each attraction is too great a burden for any business and the ADA doesn't allow businesses to go into the disability anyway - so the choice under the ADA is to accept a person's representations and give them a return time or accommodate them the best way possible with accommodations in line. Disney will have statistics and actual evidence to show what is happening with RTQ if someone challenges it and, as stated above, the person saying it was necessary is going to have to prove it with hard evidence to a court. If plaintiffs establish RTQ is necessary, then the analysis shifts to whether providing it would cause a fundamental alteration in the services Disney provides to its guests - which now includes selling line-skips to both disabled and non disabled people.
So limiting DAS to conditions like autism and the like, which by their very nature make standing in line impossible, is the way Disney has chosen to go. If a person with autism or a developmental disability is denied DAS and sued (almost an inevitability), that particular plaintiff will have to introduce the type of evidence introduced by A.L.
