MoltenGL is a thing, but that currently would put you on par in terms of features with an outdated mobile GPU (or WebGL 1). You can do much more with OpenGL as it exists on the Mac right now.
On the other hand, if Blender supports ES2 as a minimum going forward, then that should be an easy-to-implement fallback.
If and when OpenGL actually is dropped from Mac OS, the situation is probably going to be different anyway.