The problem with true multi-tasking is resource management. It’s not that much of a concern when you have a very large battery or constant power source but, on a phone, it does matter. I understand android offers this (at least in some implementation) but it just doesn’t seem practical to me for my phone usage.
When it comes to my phone, which is my communication tool first, I want to use it, at will, any time, everyday, all day without worrying about killing/monitoring background apps. In fact, I am not sure how I would benefit from true multitasking in my phone v. the current implementation (which I feel covers most scenarios efficiently and effectively).
That said, I see a benefit from bringing some of the iPad features over (horizontal split screen and PIP).
True iPad multitasking would be welcome though.