p3eps: Might I ask, where are you going to purchase your retrofit RNS 510 from so that it has this latest firmware?
I suppose this can also be installed via an update disc if one can source it. 
Its under my desk as I type! I bought it about 4 months ago from ebay.
Relaible source... hmmm... Its from Lithuania

The guy said it was from a written off car, but who REALLY knows?!
As long as you buy a 'C version' unit, you can upgrade the firmware without any problems. Its just a case of downloading and burning it onto a disk - then put it in and leave it for 50mins.
If you want new firmware, check out
www.my-gti.com