@brion @mcc Also FWIW there was precedent in ActionScript 3, which adopted a similar design for Molehill/Stage3D, and remember AS3 was going to form the basis of ES4 until Microsoft nixed it. And AS3 had a bytecode VM, which would have been included in browsers as part of ES4.
(In hindsight I'm glad we got ES6 and WebASM instead but that's where a lot of these things originate.)