I wonder if it's possible to create a GUI for the iPhone home screen when an app is used?
Since I guess the answer is no (it was in the past, havn't found anything new about iOS 7): if I have an audio player, would it be possible to kind of 'route' it to the homescreen like the Podcasts app does it? I have looked for answers but only came across jailbroken solutions so far.
Is there anything one can do there? Thanks in advance.
No, the latest SDK (iOS 7.0) does not allow this, as in add custom GUI element to the lock screen. You can let the media player controls interact with your app if you are playing audio in the background.
And use the MPNowPlayingInfoCenter to display track, artist name and cover art on the lockscreen.