There is no chance of the 4 getting dynamic wallpapers in any future revision of iOS 7. The reason why is because the GPU is simply not efficient enough to give a good user experience. In this case, dynamic wallpapers would make the home screen and transitions very choppy. This was a common problem with Android's live wallpaper on devices with older hardware and those not running Jelly Bean. You may notice some other things missing, like the Gaussian blur of Notification and Control Center. The iPhone 4 just can't muster the processing power to make it not look crappy. This was left of the iPad 2 and 3, for reasons I can't understand though.