RR can work quite well as the physical buttons you have can be mapped to almost anything, even different ones on different screens.
The iDrive skins are designed to be able to work with keyboard arrow controls (or mapped buttons/keys) to move around.
The BMW screns don't tend to be standard size (normally 6.5" as opposed to 7") so getting a touch screen to work wouldbe tricky.
However have a look for a thread by Sama, he did a lot of work getting a carPC to work with his M3 OEM system, including a capacitive touch screen.
Also look at the work by bes51659