Detect which app is in foreground on iOS9 without jailbreak
Unfortunately, I was looking for a similar solution and have come to the conclusion that, at least at this point in time, there are no known methods that will allow you to determine app usage on iOS. Even the MDM providers such as Good, Airwatch, MobileIron, etc. don't seem to be able to do this. If anyone is able to come up with a solution, I'd love to see it.
For now, however, I think we would have seen a solution if someone had one that worked on the latest iOS.
sysctl is still open but they block certain combinations of selectors. I did this on iOS 7 and gave Apple Product Security the code. They won't patch iOS 7 but rely on App Review. iPhone 4 is wide open.