seoskunk, I'm not completely sure from your question whether you're talking about the kind of "Accessibility" that requires us to make websites accessible to visually and hearing impaired users, as mandated eg by the Americans with Disabilities Act...
...or whether you're talking about search engine "Accessibility", in the sense of requiring alternative noscript html text or alt text on images, Flash, and other rich media content so engines can understand page content for indexing.
I think both are related, and that they require special care in order to work.
Regarding the Americans with Disabilities Act, your timing is particularly apt. A landmark case, I believe the first court settlement under this Act, which had gotten kicked around for some years until this case, was recently settled (amicably) in Florida.
The case has set off some waves among lawyers and site developers, and, if you have a site of any prominence, with a bunch of new law suits coming, I don't think you can afford to ignore the ramifications of the case (nor do I think most companies would want to). Here's an article about the case... A blind customer couldn't use Winn-Dixie's website. He sued. Changes are coming June 13, 2017
A Miami federal judge has ruled that Winn-Dixie violated the Americans with Disabilities Act by failing to make its website accessible to blind and visually impaired users.
In a landmark win for civil rights advocates on Monday, the Jacksonville, Florida-based grocery and pharmacy chain has set aside $250,000 to revamp its online site and was ordered to pay the plaintiff’s legal fees....
I don't know whether the ADA applies outside of US borders, but I'm guessing that for sites crossing borders it might. Compliance with the ADA is something I would pay attention to. W3C has devoted a lot of effort toward making sites accessible to special readers, etc.
Here's an article where Google provides an overview of the types of UI components affected by different types of user challenges. You might want to check it out. I know there are others as well.... Accessible UI Components For The Web Jul 22, 2016
Addy Osmani - Staff Engineer at Google
We've got a forum on Accessibility and Usability
...] ...and it's possible that this thread might yet get moved there.
The other scenario, for search engines...
Let's face it Flash sites were far cooler back in the day but yet we were encouraged to make our sites Accessible and rewarded by better SE positions for it. I think now it was just about recording activity online and this was easier to do on an Accessible framework. I think we were fed bs.
Well, let's agree to disagree. While initially I found some Flash site intros pretty jazzy compared to blinking gifs, they didn't wear well. The Flash intros were generaly built into splash pages, and splash pages also didn't wear well. They were unnecessarily interruptions, unfriendly both to search engines and ultimately to users. Once the novely wore off... IMO, waiting for logos and lettering to dance around the screen became tiresome.
I also saw a lot of sites that were built entirely in Flash with the belief that Flash could be optimized, and while some were really beautifu, in truth they were impossible to optimize for anything competitive. I saw hundreds of thousands of dollars go down the drain as they tried. I doubt that the engines were sabotaging these so they could collect information. Google worked very hard to read rich media technologies, and I don't think that Flash was ever made really SEO friendly.
Optional Flash animations within a site could be a different thing, and I directed some Flash cartoons, which were a lot of fun... and one of my designers built some wonderful product demonstrations using Flash models. These, though, didn't need to be indexed. Ferry Halim's "Orisinal" games, all built in Flash [ferryhalim.com
...] were one of the early joys of the web, and I hope they can easily be ported to another format.
Flash has, though, become a security PITA and a resource hog on battery devices, and its prohibition on iPhones will ultimately, I hope, cause its demise.
I think now it was just about recording activity online and this was easier to do on an Accessible framework. I think we were fed bs.
Google says that it can now crawl and index AJAX states, but I wouldn't depend on it where SEO is important. I don't think that Google is holding back on these... I think it's doing the best it can, and that it's not as good or as easy as you suggest.