Add a way to create custom passes

I have wanted that for a While in Blender, knowing that other softwares allow it. It would be great to have a way to create customized passes that would be completely user-made.

I thought of some ways this could work, here's the one that I liked the most:

Pass "materials", a new component that would be attached to objects that need the said new pass, would be node based like materials, but instead of appearing at render, they would appear in the compositing input of the rendered image. It could perhaps also take some of what geo nodes groups have added to Blender to its advantage!

There are surely other ways to achieve this kind of functionality, either way I would really like something like this integrated to Blender, so I can finally stop rendering the same scene 10 times just for custom passes! :D