getLayoutMap(), which Mozilla and Apple initially determined carried a significant fingerprinting risk. I don't know if Apple's position or the spec changed, but caniuse says Safari's Technology Preview does support it, so it's apparently coming there soon.
This is one of the big reasons why I am not on board with the webapp train. In order for them to be realistic replacements for real applications, the API would have to be very robust. And a very robust API comes with serious privacy issues.
The web is far too hostile of a place to allow exposure of a robust API to it.
