Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
iOS 12 is available (as of Monday 17 September)
Today's announcement confirmed 17 September release of iOS 12. https://www.apple.com/ios/ios-12/
So for everyone with paid gigs or critical work, update this weekend to the "final iOS 11" which is I think 11.4.1 and then turn off your auto-updates for iOS. You never know what will go wrong with a new iOS.
For the rest of us, yah I think I'm going for it. I'll be impressed if iOS 12 actually improves performance on my older devices.
[EDIT thread title, now that it is here.]