partially variable materials

The basic idea for this is that instead of having to work through the whole multi-user material process, we could assign a particular node, or a texture, or anything to that matter as a variable.

Use case: Say you've assigned the same procedural material to two different objects, and you want to change the scale of the texture on one object. In the default material, we'd have to make each material single-user, and then modify whatever we want.

My proposal is that we should be able to assign specific nodes or textures as "variables" so that we can have the same material on multiple objects, but each object will have its own control over the material.

I've assigned the same material to these six planes. If I weren't planning on changing the material at all, that is fine.

Now, I have made each material single-user and changed the colors. But now if I wanted to change the golden pattern on them, I'll have to individually change the values of all the materials.

Interestingly, I thought using node groups fixes this problem, because if I change a value in a node group inside a material, it should change the values in the other materials where it is present, right? It does not. Even if the node group is multi-user, it doesn't make any change unless the actual material is multi user.

TL;DR We should be able to assign specific nodes in a material/node setup as "variables" so that the multiple objects have control over specific things even though they utilise the sane material.