Imagine starting from scratch with Genode or what Google is doing with their new (3rd) OS.
I agree that's important, but I don't think that a great OS should become just a good OS in pursuit of that goal. After the OS is made, it seems like there would absolutely be ways to make the system accessible as-needed.
Most of the standard conviences available to "normal" people because smartphones are a thing and yadda is how I make my life work.
Among other things, I also co-own a tiny list for blind developers. So I have some familiarity with the fact that there are people who actually need accessible design in a way that I don't.
But I think any internet that works well dramatically improves life for the vast majority of the 60 percent of people who have varying degrees of impairment, two-thirds of whom do not self identify as disabled or handicapped.
Cars were invented for people with sufficient use of their limbs and eyesight. After their invention, the control systems were adapted for people who, for instance, can't use their legs. I don't know of any way they have been adapted for e.g. blind people. And yet, even though they are not accessible to a large fraction of disabled people, the world is better off with cars, designed for not-disabled people and then adapted as far as possible, than without cars.
That's all I'm getting at. Its too much of a constraint on invention, but likely to be adaptable later.
B. If it wasn't clear, I'm generally on your side here.
Really? All? And if not all, are we back to the ADA reasonable accommodation standard? What bugs me about the "accessible or bust" people is that they will deprive 99% of the population of something because 1% can't have it. There's some on-going case about university courses in California of some sort being publicly released but "not being accessible". So now, no one can access it because they got taken to court. It costs zero dollars (or very few) to publish existing material to the world; it costs quite a bit more to add stuff to it.
Maybe a great OS should be available which can run quickly without accessibility features, but slower if they are explicitly installed by an end user. Like it or not, it's a balancing act between how much we're willing to give up and for how few people.
To be sure, software does have some bloat. But some of the complexity is necessary for software that can be used by the whole world.