From a legal perspective, the only pertinent question is whether the accommodation Disney is offering is "reasonable" within the meaning of the ADA -- and if it is not, whether a more "reasonable" accommodation would force Disney to change the nature of its business. In other words, is allowing persons with disabilities that make it difficult for them to endure waits to be excused from waiting in line (but not necessarily excused from waiting for an attraction altogether) a reasonable accommodation for their disability? If there is a more reasonable accommodation available (e.g., giving every person who says they "can't wait" a front-of-the-line-pass for every attraction they desire), then would Disney be required to alter the nature of its business in order to give that accommodation to disabled guests?
As I see it, the present accommodation is reasonable. Is it ideal for those with disabilities that require instant gratification in order to avoid becoming agitated, or whose disability deprives them of the stamina typically required for park touring? Of course not, and no one should question or downplay the legitimacy of those needs, but giving "waiting-disabled" guests the accommodation of a "deferred Fastpass" for every single attraction so that they may spend their "wait time" resting or amusing themselves elsewhere is reasonable. To provide more (that is, to provide instant front-of-the-line or Fastpass-queue access on demand) would require Disney, a theme park business operating on a "first come, first served" basis intended to provide maximum opportunity for every guest, to "fundamentally alter the nature of its business." One of the legal definitions of a "fundamental alteration" is the requirement that a business offer a different "product" to disabled customers than it offers to non-disabled customers. (In a world where guests at many theme parks pay extra to gain front-of-the-line or Fastpass-style access, clearly that level of access is a "product" of measurable value.) Thus, to compel Disney to offer little-or-no-wait access to disabled customers but not non-disabled customers would result in a "fundamental alteration" of its business for purposes of the ADA. As such, it's something Disney cannot be required to do.
Consider for a moment the logical consequences if a court were to hold otherwise. If, in fact, the court overseeing this current lawsuit concluded as a matter of law that the only reasonable accommodation Disney could make would be to offer instant, little-or-no-wait attraction access to anyone who claimed an inability to wait, and that requiring Disney to do so would not alter the nature of its business, then that legal precedent would mean that all places of public accommodation that typically offer services on a "first come, first served" basis -- every fast food restaurant, every movie theater, every grocery and department store checkout counter, every concert ticket vendor, every airport taxi service, etc. -- would be required to provide instant, front-of-the-line access to any person claiming an inability to wait for service because of a disability. We see the absurdity of that -- there is no reason to compel a different result when we're talking about theme park attractions.
I sympathize with the plaintiffs here -- they had a system that was more friendly to them, a system that went far above and beyond what the law required, and it's been taken away -- but there is nothing unlawful about what Disney did.