I think 3D in Construct is mostly to add "flavor" to 2D games.
I had a great deal of fun putting together my retro-3D game "Vault of Peril" but it is, essentially, a glorified 2D game looking from a different angle. And there's not much future in that other than as a curio since people have played better for decades. As simply a game-making hobbyist I can't go any further than the trial allows (a fun, game-like challenge in and of itself), but even having unlimited Construct resources would not get me, personally, much further with my ability level. And someone with professional skills wanting to build even a decidedly retro-looking 3D game would most likely choose another engine.
But, as mentioned, it was a whole lot of fun and as a non-programmer I don't know how I could have done it without the event system (and I still lurk here).
construct.net/en/free-online-games/vault-peril-32857/play