Hello!
Currently, there are no plans to support 3D weapons or characters since it's aiming strictly for a retro, sprite based shooter feel like Build Engine and DOOM Engine.
That said, even though the template goal is to be drag & drop with no need to code, the foundation is still flexible enough that you could implement your own 3D assets with some manual setup and tinkering if you have experience with the Godot engine.
This would be cool but since the template is strictly designed around 2D sprites, adding full 3D model support would require significant changes to the core logic and resource framework.
Because of this, it won't be covered in the official guide. However, if you're comfortable editing GDScript, you could theoretically attach a 3D mesh node to the enemy/weapon scene and hide the main sprite node as a workaround.
If I ever get a chance, I might drop a guide for it.
