[zdragnar]

I'm not aware of any general requirements for software, aside from what the ADA covers and case law. The most common example I know of is Target; IIRC it was among the first to bridge the real world and the internet in terms of legal requirements for accessibility. [0]

What it largely boils down to, from a legal (not necessarily a moral) standpoint is the balance between "reasonable accommodations" for the disabled and "undue burden" on the business to implement accommodations.

When you're small and scrappy, or dealing with some domain that absolutely demands unimpared vision to use, you can argue that accessibility features would place some undue burden on the business to implement. As you grow larger as a company, and the very likely probability that what you do doesn't actually absolutely need unimpared vision, the more likely a judge or jury would be to find that accessibility features would represent a "reasonable accommodation" that you must fulfill, and likely must pay a lot of money for failing to have done so.

SaaS applications almost invariably can be made accessible, since they are, by definition, provided as a service over http or some API. Whether you must make them accessible is for a court to decide; whether you should is almost always a yes. It's generally cheaper up front than paying the legal cost later on, and your users will appreciate it. You may even end up hiring a blind engineer, who would most certainly appreciate it.

[0] https://webaim.org/blog/target-lawsuit-settled/