People who need accessibility should have a tool like this automatically injected into all of their sites (since, even if you believe all sites should add this,

People who need accessibility should have a tool like this automatically injected into all of their sites (since, even if you believe all sites should add this, many are simply not going to, so it will need to be injected anyways). The real benefit IMO is if you can provide customization to the accessibility tool, so that a) they don't break your website, and b) you can add new custom tools if necessary. Without necessarily including the tool itself (though if you do need to include the tool to customize it that's ok). Then people who inject your accessibility tool will get access to that customization, and it will provide them a greatly enhanced experience. And if enough people join and you're lucky, it can become standardized and widely adopted, like ARIA.