Do what you do best. The primary reason why Construct is such a damn good 2d game engine is because the developers focus on developing a well thought out 2d game engine.
Adding full 3d would only confuse matters, and they would have to compete in a very different market. That market is quite saturated at this point.
So no: the right tool for the right job - if you want full 3d, go with Unity, or another 3d engine.