OK, so the powertrain needs to have an realtime OS, there is no way around it. You need to measure lots of parameters like air mass stream, temperatures, exhaust oxygen, etc, in realtime, process the data and output to the gas pump, ignition system and such extremely time sensitive devices.
And now have the infotainment system playing a movie in the rear seat, the other rear seat maybe plays a game and on the drivers seat you have navigation, OSD and display data. OK, now you have a little bit of lag in any of your infotainment system... gues what happens to the powertrain??
This is the same reason why you cant have a raspberry pi on RT Linux have run a 3D printer, many have tried and it just does not work properly... if even such a system cant be built, I wish VW good luck with the Car OS... even though I am german...