In The Verge Forums, A User Mocks Up A Way To Quickly Clear All Apps Out Of The iOS Multitasking Tray
I think this is just patchworking over a deeper issue in the iOS multitasking metaphor. The underlying problem is that too many users perceive the multitasking tray as a queue, when it is meant as a history.
Rather than making it easier to declutter all apps at once, Apple needs to stop users from feeling like they have to clean out the tray; in an ideal design for multitasking a compulsion to “declutter” wouldn’t exist.
Of course, WebOS’ cards metaphor relied on constant maintenance by the user to swipe away cards. I would argue there is a distinction though, as it was a gradual process — cards didn’t ‘pile up’ so it didn’t feel like a chore to swipe them away one by one.