I'm thinking well beyond this level. Instead, the ability to have the same application running, but with two different user interfaces, depending on how it is being used at any particular time (desktop vs mobile), and optimising resources accordingly.

I see the appeal of full multitasking, but most of the time people —*including myself —*would rather not have to go to the bother of working out which background processes are sucking up all the juice. The iPhone's model works reasonably well for the majority of multitasking activities and battery usage is reasonably predictable. Where my N9 can quite suddenly suck through its battery, and you have to do a bit of debugging to work out what is doing it.