The fact that web developers will then need to worry about differing implementations across browsers and -- pray not -- across blink versions, on the other hand

The fact that web developers will then need to worry about differing implementations across browsers and -- pray not -- across blink versions, on the other hand, is not hyperbole. If it's ready to ship with nobody else agreeing on how it should work, please do everyone a favor and ship it with a prefix. If only as a courtesy to fellow developers who will need to deal with this mess. Nevermind that you don't want a prefix. Use one. Better prefix hell than different implementations using the same syntax.