lt might not be as simple as retro-fitting a part to current cars, especially if the new hardware is a different design to the current infotainment screen.
The linked article in the first post in this discussion topic states that new hardware will be installed ‘within the next 18 months’, so I suspect installation of new hardware with illuminated slider controls may coincide with a model’s mid life facelift. That gives VAG the opportunity to change the design e.g. to also incorporate a
lower row of physical buttons seen in the pictures in the linked article; if they do change the design, then parts may not be readily interchangeable between the current hardware in existing cars and any new redesigned version.