That's exactly what BMW's iDrive Touch is. A track pad on the top of the iDrive knob.
Sorry, but I don't really keep up to date on what BMTroubleU does. I'm a Mercedes kind of person. That's what I prefer. Nothing personal, I just find I fit better in a Mercedes. I've had friends that let me drive their older Bimmers and I never liked the ergonomics, everyone has their own favorite as far as what feels best for their body type. I can't stand Japanese cars and never felt right in any of them that I've been in. Same goes with US cars.