The data and PD communication are both working (that was the majority challenge on the EE side, shown in his video). So it would depend on the capability of his solution to let the phone work in host mode, thus being able to provide power to the adapter.

Though I'm also not sure how the MFi situation is with those generations of iPhones, and what restrictions Apple has built in to the OS. I haven't worked with MFi for a while, and I don't know for sure if MFi chips are even required anymore for that generation of lightning devices, or whether the author has incorporated one.

EDIT: I just saw this on his website:

> Any other accessory that requires power from the phone is not compatible.

So no, USB-C to headphone adapters won't work, they need power.