Regarding iOS 8 Multitasking

Based on the video posted by Steven Troughton-Smith, I think there are huge benefits with such a feature. The Safari interface, for instance, turns from an iPad interface to an iPhone one when you shrink it by half. But I have several questions:

- iOS might already do this, but to what extent can it scale apps currently?

- If this feature is released in iOS 8/ 8.1, will it be identical to Android's/Windows 8's functionality?

- When the app has a custom UI e.g. Twitter for iPhone vs iPad, you would have to change the interface from the one with the bottom bar to one for the iPad. Could this make navigation confusing?

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- Finally, will this possibly increase the app file size because you're downloading both sizes?

I think this feature is exciting when done right, and could push for better designs that are scalable, just like responsive design for the web, but could this limit the way devs design the apps?