Some WebGL developers have pointed out that the instancing support both in WebGL 2.0 and in WebGL 1.0's instancing extension are missing some alternate entry points which would make them more efficient.

https://github.com/KhronosGroup/WebGL/issues/2526 requests the BaseInstance variant of instanced draw calls, and https://github.com/KhronosGroup/WebGL/issues/2434 requests the BaseVertex variant of these calls.

Feedback has recently been received from some WebGL users that multi-draw functionality is important to increase the possibility of batching, which is being investigated in Issue 890539. Perhaps during that investigation, we could see whether it's possible to subsume some of this functionality, or whether we should add a separate extension.