I'm curious as to the scope of the problem, if html spec drops xslt, what the solutions would be; I've never really used xslt (once maybe, 20 years ago). In addition to just pre-rendering your webpage server-side, I assume another possible solution is some javascript library that does the transformations, if it needed to be client-side?
>very, very few websites
Doesn't include all the corporate web sites that they are probably blocked from getting such telemetry for. These are the users that are pushing back.