Guidance to Implementing Draw Material to Volume Render Target?

Hi everyone,
I googled around and it seems like “Draw Material to Volume Render Target” isn’t implemented yet.
I want to utilize my C++/HLSL experience(enough to understand Godot source code) to implement it and I want to dirty my hand quick.

Can anyone provide some guidance to Implementing Draw Material to Volume Render Target?
Or shall I make my own material system that can read and write a same 3D array?

Any advice will help so please generously reply if you have any thoughts!
Thanks in advance!