Is it possible to mask movieClip in webgl mode ? Other webgl librairies like pixijs have that possibility.
I have also watch the video of an introduction of animate cc (The Future of WebGL with Adobe Animate & AwayJS | SkillsCast | 9th February 2016) where the presenter talks about it.
I watched the part where the masking failed. He may have made the AwayJS FLA by converting another file format. Or he had a bug in their custom file format at the time.
Masks in the WebGL 2D FLAs seems to still be disabled. But, I just acquired the AwayJS add-on, and whatever the problem was in his demo, it seems to be fixed, masking is working.
Go here to acquire the add-on:
I didn't checked the add-on and you are right, it's working.