Sorry but they just released lightning headphones and the lightning audio adapter. They won't switch that fast.
You mean the free with iPhone 7 purchase, $9 Lightning to 3.5mm adapter, and the Lightning headphones that are not supported on any other non-Lightning equipped device?
Apple will drop Lightning as fast as they can, but not for USB-C. They'll drop Lightning when wireless charging becomes a practical reality, and adopt something like the SmartConnector for physical wired connections as needed, and yes there will be a new connector to Lightning adapter when that happens to support those limited-use Lightning headphones and even those free/cheap 3.5mm adapters, assuming anyone will still want to use them.
And rumor has it that could happen as early as this year.