"is it not possible for the GPS manufacturers to program the missed approach procedure into the GPS"
Sure but I
suspect that the problem is that the # of pro-GPS people in the respective national CAAs is still vastly outnumbered by the former navigators retired from the respective national Air Forces
"There is no way that you can couple an autopilot in both VNAV and LNAV with current systems such as the G1000"
There is a real crude hack of a KAP140 (or 150?) in the DA40/42 that I saw on the ground. Such a waste of technology. Auto throttles would be a bit of a certification problem, I would think - have they ever been certified on a piston aircraft?
"This is why the CAA are about to bring in differences training for glass cockpits and also for single power lever control"
The glass panels don't have additional functionality over a full complement of standard IFR avionics, so I don't know why this will be needed. Unless you want to argue that official diff training should be required for flying anything half decently equipped, which I would agree with