This would be orthogonal to parametric and timeline design but another thing that gives people much more power when it comes to mutating their designs later in the process.
Instead of having joins irreversibly combine geometries, why not retain all of the ingredients, boolean operations, and finishing steps, and then let us move the sub-components without having to roll back and forth in the timeline ?
We should still be able to export the same final components and assemblies to other programs, but internally we’d be able to move things around easily and immediately see the results.