Earlier quoted context omitted.
Those 1 in 10 users don't provide enough revenue to warrant doubling our front end budget to support every polyfill, every workaround for every non-polyfillable thing, and the vast quantities of extra support they require. If they do in your case, though, I understand.
So I guess following your point, accessibility should not be a thing, on or offline.
You're limiting 'accessibility' to the current 'boil the ocean' approach pushed by the accessibility industry, which has a perverse profit incentive in the problem not being solved.
Accessibility is better addressed in the client than in the server.