So, giving this job to Fortune500 companies is demonstratably not sustainable. A single higher up can terminate such projects with the wink of an eye.
I was more hopeful 20 years ago. Then I watched how all the good work on GNOME2 was basically trashed because of DBus transition, GTK3, and now Wayland. Fact is, hoping for the corporate world to do the work is no guarantee they will continue. And for "scratch your own itch"-philosophy to work, there are not enough disabled OSS devs. Maybe after WWIII there will be a surge in Open Source Accessibility.
Scratching our own itch works better when coordination means we can bundle together a whole lot of itch. There is no such thing as individual incentive to cooperate without a means of coordination. Anything else is just the volunteer's dilemma, and so only small itches get scratched.
Not everything can be handled using death by a thousand cuts. In the Rust in 2021 blog [1], the importance of depth versus breadth was pointed out. Depth comes from dedicated, full-time, paid work.
[1]: https://matklad.github.io/2020/09/12/rust-in-2021.html]
You can see my gloriously broken prototype at PrizeForge. Currently between iterations and still not quite viable enough to properly operate.