They had support in both Safari and Chrome, but never in FF or IE (nor Edge). Chrome eventually dropped the support.
So I'd say if you can't get all four to implement the feature then you might as well call that part of your spec a "living standard." Those features are going to get way fewer eyeballs, fewer bugfixes, fewer reviews, fewer pieces of documentation, etc.
https://caniuse.com/#feat=svg-fonts
They had support in both Safari and Chrome, but never in FF or IE (nor Edge). Chrome eventually dropped the support.
So I'd say if you can't get all four to implement the feature then you might as well call that part of your spec a "living standard." Those features are going to get way fewer eyeballs, fewer bugfixes, fewer reviews, fewer pieces of documentation, etc.