I keep thinking about pcb's file (and thus data) format. I have lots of ideas but no traction :-(

Some ideas:

Elements should be able to reference a common footprint or copy it to make a private footprint (sketchup does this a LOT). I.e. all DIP16 elements should share a common footprint, and editing one should edit them all. Note we have the "inhereted attributes" problem all over again, like gschem - the footprint provides a default refdes location but nearly every element changes it, but that shouldn't mean needing a private footprint definition for each element.

Likewise, footprints should reference a common set of padstacks, rather than have N independent but identical padstacks. There should be a way of overriding part of a padstack without having a private copy of it?

These "common" definitions should be somewhat independent of the layer stackup (i.e. symbolic layer types) and map to the specific layer stackup somehow. This lets developers change the stackup without worrying about the footprints, and maybe opens the way to flex cables where different regions have different stackups.

PCB should have a concept of a "sublayout" (i.e. four identical input channels). Sublayouts should be movable, rotatable, go on either board size, yet if you edit a common one, they all change. Sublayouts should somehow relate to heirarchical schematics, including some rules about how to name/rename parts within.

Footprints should be a sublayout :-)