A global variables system that can be referenced from anywhere in Blender.

You do some math in Geometry node, and if you want to use the result elsewhere (especially as a driver), you can't. the best you can do is to store that data as attribute on something, but those can't be used as drivers, and will be visible to only the assigned thing (geometry, instance etc...).

The idea is a new node in GN, that would look like the AOV node in shader editor, to store data, and you will be able to use this everywhere in blender, in any editor or driver, and in every scene as well.

setting up such a variable should be possible from geo node, and also from a dedicated new editor (global variables editor) where you can do math inside to mix those variables freely, and save the result as new global variables.

I believe that other 3D softs (like Maya or cinema 4D) have a feature like this.