Even if Construct 3 did have a 3D environment. It still would most likely be that Unity 3D would still have the better 3D environment, because the Unity Team are experts on 3D as the Construct Team are experts on regards to HTML5 2D.
If you want more 2.5D support, then Construct 3 might get that. But that maybe is still in the long future and it would also be pretty limited. It may not be the 3D environment you expect, it may just be for handling support with Top-View perspectives.