Dropping the jack has nothing to do with old or new technology.. The simple face was as long as it had the 3.5MM plug they could not make the phone any thinner.
Look at the iPhone 6, what is the largest opening in the case? It’s that jack and the part inside is slightly larger than the opening.. So, to make the phone thinner the jack had to go.. Nothing more complicated than that.
Apple said nothing about making it thinner now. IT is sufficiently thin. There is nothing to be gained in going thinner than it is already. Any thinner and they'd have no room for the kind of cameras they want in it.