A recent patent filing from Apple shows that they plan to merge the headphone jack and hole for the microphone into one, unified jack. This would further reduce any unnecessary openings in the phone’s housing, and make the design even more minimalistic. Don’t worry though, this patent does not say anything about a proprietary headphone connector, so you can continue to use your standard 3.5mm headphones.
This design would reduce the number of openings dust could potentially get into, and be more aesthetically pleasing. It’s possible that they will also introduce this design into the iPad or MacBook.