I see 3 potential options:
a) Make use of simple custom physics, while manually using shape collision functions, and checking if entities are on the same Y plane (more like an interval of Y values). But all those pre-built physics of Godot cannot be used, and they are very handy.
b) Hack around with Godot's physics. Is there a way it would work? For example, how to still have the auto collision detection and resolution taking place by using kinematic/rigid/static bodies, but only if the elements are on the same Y plane?
c) Use 3D space + Orthogonal Projection + 2D elements. I made a basic scene, though I could not have the camera looking "right" and... well it's 3D, more complicated I guess, and there isn't as much documentation.
Are any of those options doable? Are there other ways?
edit: I am mentioning physics quite a bit, but I actually wanted to mean auto collision detection and resolution of using PhysicsBody2D (like a Kinematic or Static body) nodes.