Apple has been very good at predicting (or perhaps directly causing) the demise of certain technologies: the disk drive, the CD drive, the ethernet port. They removed them much to the chagrin of many a loyal customer, and a few years later they nearly ceased to exist across the entire industry (we're still waiting on the ethernet port to go away but give it time).
How many times will it take you forgetting your dongle to just pony up and buy the apple approved headphones? How long will it take you using the non-default, non-apple, non-sleek, clunky dongle as you show off your fancy new iPhone 7 to your friends before you decide it's got to go? What if they're using it the apple-intended way?
How long will it take before nobody buys headphones anymore? A few generations until they deprecate the dongle since nobody is using it? Where you can no longer buy a $10 set of headphones at a drugstore and plug them in? Where 'every audio device must provide analog audio output in a universal format that every device has been able to read since audio was invented or it is functionally useless' is no longer a maxim?
Long-term, we are giving up a universal and open protocol that all devices work with for a proprietary one. If you don't expect companies to abuse this to make money and to stop you from doing what you want with your equipment, well, I've got a bridge to sell you.