Given the quality of today's wireless audio devices, and the slowdown in Moore's law, I don't see any replacement for the venerable headphone jack. Like TCP, it's a solved problem.
1) You need an analogue stage somewhere to produce audio; 2) Is it really that large? On my Lumia 950, the battery is virtually as wide as the headphone jack, and the camera lens protrudes from the main body of the phone already.
For those reasons, I'm not convinced a smaller headphone jack is particularly necessary.
Hell, Apple was first to ditch floppy drives, CD drives (some models), ethernet ports (some models), and Flash. They've got a pretty good track record of "we don't need this shit" lately.