Pixi.js 3D features are meant to be light, so you wouldn't be able to do massive 3D games with them but you could use it to clone old school 3d games pre ps2. The 3D limitations are quite severe but understandable since it's a 2D framework.
3D is easier with MV than previous makers, what exactly are you trying to accomplish?
There's no 3D hardware acceleration tho which sucks :(
Well, no this is mostly wrong.
PIXI.js has 3D hardware acceleration when available, that is definitely true. And
because of this, it can do full 3D graphics that's at the quality of current 2017 generation games, not pre-PS2 as suggested here. But when it isn't available (which is becoming less frequent) then you're stuck with 90s era software rendering, which I've done a few experiments with in RPG Maker MV, you can even see one of my experiments with software rendering here:
https://goo.gl/U0lSj6
A CPU with a fast clock is needed for that demo due to it not using hardware acceleration.
You can definitely make a full-3D game in MV, just that you'll need to do a fair amount of work to get that set up in RPG Maker MV. I've done small tests and experiments, it's entirely possible, but when depending on hardware acceleration you will lose compatibility with some devices, mostly low-end Android phones right now; hence my software rendering investigations as a fall-back option.
I have plans to make a 3D graphics Plugin (I mentioned an API earlier in this thread, but I think a full implementation is what the MV community wants), but I want to get pixel-movement done first so the demo can show full rotating 3D models walking around the map.