For what it’s worth (absolutely nothing), here’s my guess: The next iPhone will ship with earbud headphones that connect using Lightning. There will be a separate 3.5mm-to-Lightning connector available at an Apple-like price (not necessarily cheap). There will be an Apple-branded, over-the-ear headphone that will match the design of the phone that is bluetooth capable and can be charged via Lightning connection.
(footnotes) Some history to support these guesses: 1. Apple is willing to ditch things as they believe necessary, for example, USB, ethernet, disc drives. 2. My latest (last?) MacBook Air updated charger connection and I was able to buy a dongle to use the charger pack from the previous generation. 3. Apple continues to offer more and more separate branded additions to their line. Available at their online store right now: protective cases, keyboards, smart covers, batteries, mice, trackpad, keypads, adaptors, cables, docks, watch bands, and a Pencil. Guess how many Apple brand over-ear headphones are currently available?