In my dream world, Apple would make some sort of standardized bluetooth receiver similar to AirPods minus the actual audio hardware. It would just be the transceiver, electronics, sensors, and DAC. Then you could attach it (via e.g. a UE or Shure audio cable connector) to whatever IEMs you wanted.
This would not only address the fact that the actual audio on apple buds is very mediocre, but would also allow for some separation of concerns and easier replaceability/customizability.
I am pretty sure the correct answer is: Stop making phones so thing and bring back the 3.5 headphone jack.
If the 3.5 really is a hindrance, come up with a connector that allows a simple adaptor to 3.5 jacks and still allows cabled charging. I already have a couple of L-adaptors for my headphones with straight connectors, so carrying a 3.5-to-Lightning doesn't bother me. But not being able to charge at the same time. WTF?
The thinness wasn't the problem - there are hundreds of phones thinner than an iPhone 7 that still have the 3.5mm jack (e.g. Galaxy A8 is 5.9mm compared to iPhone 7's 7.1mm).
The problem was the increased space required for the taptic engine.
This would not only address the fact that the actual audio on apple buds is very mediocre, but would also allow for some separation of concerns and easier replaceability/customizability.