Mot sure if this help...
I retrofitted an MDI unit when I installed my RNS510. The wiring harness I got was PnP, and the place I got it did not ask whether I had an RNS or RCD. After the retrofit, the MDI works 100%...
As for updating, there are firmware updates on my-gti.com. The module seems to have only been changed this year, and it's the first time there has been a firmware update that is for MY 2012 only.