As long as there's an adapter that provides a headphone jack, I don't see a problem in removing the onboard headphone jack.
The bigger problem lies with the use of Lightning to begin with, rather than a standard like USB type-C. That would solve the power problem: adapters exist to split out power and other ports from a single type-C port. It would also solve the "only works with" problem, since normal USB headphones would work, or analog-over-type-C devices; that, unfortunately, makes it far less likely to happen on an iDevice.
I look forward to incredibly thin Android devices with nothing except type-C, though.
The bigger problem lies with the use of Lightning to begin with, rather than a standard like USB type-C. That would solve the power problem: adapters exist to split out power and other ports from a single type-C port. It would also solve the "only works with" problem, since normal USB headphones would work, or analog-over-type-C devices; that, unfortunately, makes it far less likely to happen on an iDevice.
I look forward to incredibly thin Android devices with nothing except type-C, though.