Just to report, got my OTG cable today, and have tested it with an iPhone 6s running iOS 11 Beta 4 and it appears to work fine - too windy here for a test flight at the moment, and it did take 3 attempts to connect and get the 'unsupported accessory' message.
Still, looks good for working with iOS 11 for those that were interested

Also running iOS 11 Beta 4 on an iPhone 5S.  I've always gotten the unsupported accessory message, whether on iOS 10 or 11, but as long as I plug the phone in first and then the controller, it's worked every time.

virtguy Posted at 2017-7-28 07:36
Also running iOS 11 Beta 4 on an iPhone 5S.  I've always gotten the unsupported accessory message, whether on iOS 10 or 11, but as long as I plug the phone in first and then the controller, it's worked every time.

66% of the time, it works every time.

iPhone 7 plus with iOS 11 Beta 3, and no issues flying with the OTG adapter to the controller.  Good to go so far!

Ha on IPhone 6s 10.2 Jailbreak and disabled the stupid pop up for unsupported accessory