Yeah, but let's not just focus on the end of life of the Flash plugin in 2020. As I say in my previous post, it's the whole of everything.
In relation to the low power of as3 for 3d, it is true, but I also think that it was a "minor" impediment compared to the rest of the factors.
I give an example: in Flash in 2d you can do very good things, but never at the level of C ++. In 3d it could be the same. Productions of good quality but without reaching the levels of a maximum level3d engine (Unity or C ++).
I think we did not remember the stage3d boom in its early years ... There were lots of 3d things. 3d engines, applications, games in browsers, etc ... The abandonment of all that, was mainly for the whole set of decisions, and not so much for the limited power of the language + runtime (in addition, that at that time there was a plan for a new AVM / new language - that is, we would have more runtime speed).