There's also that video of a guy adding a headphone jack in a similar fashion. I was impressed that he found the internal room for it.

I never understood why this was always seen as such a constraint. It’s three (or four) pins! It doesn’t even have to have the “hole” form factor. You could have them all in a straight line and then place a headphone jack AGAINST them. I always thought a magnetic TRRS set of pins along the side of a phone could work. Add a sleeve to the connector’s side too. Heck you could standardize a flattened TRRS or whatever that would still slip readily into a typical jack.

When you already need an adapter you might as well use the usb-c connector.

That was on the iPhone 7. Its internals really look like the decision to omit the headphone jack was made pretty late in the development cycle, so they replaced it with a useless piece of plastic.

Possibly Strange Parts: https://www.strangeparts.com/bringing-back-the-iphone-headph...