Physically the controllers are the same dimensions so that at least doesn't prevent a retrofit and also means BMW doesn't have to redesign trim elements. A software upgrade will be required, for certain. On vehicles without touch, coding can probably enable it.
The only thing that might be necessary is additional wiring, but I suspect the existing connector can transmit the touch data. It is only 4 wires (12V, GND, data in, data out) but is fully bi-directional.