"What a WebGL2 successor could look like and why it can’t be WebVulkan" - https://floooh.github.io/2016/08/13/webgl-next.html
See also the the author's sketch of a next-gen web graphics API on top of WebGL (https://floooh.github.io/2016/10/24/altai.html) which is (perhaps unsurprisingl) broadly similar to the sketch given the article (minus command queues, shader libraries, ...).