Functionally/technically I just don’t see the pro/con being in any way pro removing the aux.
pro:
more place (or they could make the phone thicker)
waterproofing (obviously also possible with the aux port)
wireless is the future (there being an aux port in no way prevents people from using wireless)
better sound quality using digital signal over the lightning connector so as to let headphones use their own DAC (there being an aux port in no way prevents people from using lightning)
con:
can’t use 99% of already existing headphones without a dongle
can’t charge phone while using the lighnting port for audio
making a big deal about usb c in the macbook and then forcing the lightning port on the iphone seems weird
from a business POV: I’m sure they crunched numbers but I’m not convinced the extra sales from dongles and headphones will be worth it