can is not the same as must ... there is absolutely the possibility of adding support as a binary implementation, especially with the relatively short turn around of green browsers. IE11 and Safari are the last of the old guard on this and mobile devices have a 2-3 year burnout in terms of support.

Not to mention it could be feature detected via browser, js and other means as an interim solution. Also, I'm pretty sure the implementation is wasm with a very thin JS shim, at least that would be my presumption as I'm not familiar with this format/project.