On the topic of improving their multi-tasking, I would really like to see the option of a button to "kill all" running apps in the background as opposed to closing each one individually.
You never had to close each app individually in the first place.
Most of the apps (unless they're playing audio or using your GPS) will just become inactive in the background so they don't use any RAM/CPU, their state was simply saved to storage so you it can resume when you switch to it again. "Killing" them had no effect except to clear their state cache.
Apple has never really made the way iOS multitasking works clear so I can't blame users who think iOS manages multitasking like a desktop, but it doesn't. It's made to manage stuff by itself. Only killing active apps has an effect, and apps are rarely active in the background unless you have a clear sign they are.