The next iphone in 2017 or 2018 probably won't have the adapter. All headphone manufacturers should go and ask for lightning certification. The adapter is just a temporary measure to soothe customers. It won't be supported forever.
If apple honestly wanted digital audio they would have used the universal USB-C standard for the future. Apple wants customer lock-in to their platform and using lightning will prevent customers from leaving because these customers have invested a lot in their ecosystem. Ditching the lightning and moving to USB-C was the right thing to do, converting everything to lightning isn't.
Apple will only drop the adapter when enough people no longer need it. And given that Apple still sells a VGA adapter for the iPhone, it's not like they are likely to stop making it any time soon.
If apple honestly wanted digital audio they would have used the universal USB-C standard for the future. Apple wants customer lock-in to their platform and using lightning will prevent customers from leaving because these customers have invested a lot in their ecosystem. Ditching the lightning and moving to USB-C was the right thing to do, converting everything to lightning isn't.