As long as we live in a competitive economy, there will be multiple user interfaces on telephones. If I pick up someone's Android, I don't know how to use the advanced features - and if they pick up my iPhone, they probably suffer the same problem. In addition to the fact that not all APPs run on all phones, this explains the justification for dual-OS Smartphones. I'm not saying that having competing operating systems is necessarily beneficial, I'm just thinking about how to deal with the reality. While phone interfaces may not be "misison critical", when they get incorporated into the operating systems of cars, there might be serious consequences if drivers cannot figure out how to operate their car.
Dual-OS systems would be very useful if there were APPs that were available for only one device or if different users were experienced with different operating systems. Elsewhere on EETimes there have been discussions of cars utilizing smartphone technologies and the problems that would develop if a driver only familiar with the "Android" interface were to rent an "iPhone" interface vehicle. Dual boot systems would solve the problem.