epub and odf didn't get embedded in everything, and they don't require extra effort to make accessible so that everyone can read them. PDF's do since they are more often than not generated via library, and since noone wants to make the effort, they're inaccessible more often than not.

And I have absolutely zero confidence that the same wouldn't be the case with any sort of portabilization of web page assets for browsers.

We have enough of an inaccessible web already, developers and designers and managers don't need another tool to make it worse.