MIDI - Custom ViewControllers and ctypes
I just learned that implementing MIDI over Bluetooth LE "requires" an app to implement a custom ViewController. This one is CABTMIDICentralViewController. If IOS sees a bluetooth LE device that provides the newly published MIDI profile, it hides the device from normal CoreBluetooth peripheral scanning. Instead you have to use this special view controller to access the list of peripherals.
The net effect for my Pythonista development is that I can't use the cb module anymore to talk to "standard" MIDI BLE devices. It still works for other devices like my LightBlue Beans and many others. However, this will likely change if Apple decides they need to take complete control of the UI used to config a specific device. This could easily happen for fitness bands and other things that become mainstream devices.
On a positive note though - I have found out that most developers who support CoreMidi on IOS are using PGMIDI to do it. It presents a very nice and easy to use wrapper to make CoreMIDI easy to implement. It is worth considering using for just getting "stock" MIDI support going.