They are simply making a whole couple of generations of headphone obsolete.
To headphone manufacturers, that is an opportunity.
Those crappy earbuds that come with iPhones never stay put. If they were not on a cord they would get lost.
Wireless? Fail, they will fall out.
It would seem easy to produce a Lightning adapter that you could plug any ordinary phones into. The phones that have a built in dedicated interface will find few uses.
Just because Apple comes out with a new phone does not mean that everyone has to convert to it by tomorrow. Unless of course it is like the ACA - if you like your iPhone 6s you can keep it. I have two sets of headphones - one wired that I keep at my desk and one wireless that I keep in my saddlebags for riding.