Headphones should all connect to a phone or laptop or other device using USB-C, not using the old 3.5-inch jack. There are several advantages to USB-C.
First, the headphone jack is a single-purpose port. Arguing for it is like arguing for a keyboard port, like the old PS/2 port. Ports should all be multipurpose, so that you have the most flexibility in using them. A device that has two ports is far more flexible if both are USB than if one is USB and the other is the headphone port, like the 12-inch Macbook.
Second, USB supplies power to headphones. Power is useful for many reasons: for noise-cancelation, to run an amp that increases sound quality, for higher volume, to charge Bluetooth headphones, or to run a graphical equaliser. Let’s take them one at a time.
Noise-cancelling headphones require power, and that means you either have to charge your headphones, or keep replacing its batteries. Nobody wants yet another device to charge. USB-powered headphones, on the other hand, draw power from the phone. This makes them far more convenient.
Besides, when some noise-cancelling headphones run out of power, they completely stop working, even as ordinary headphones. In that situation, a feature (noise-cancelation) has become a liability — you’re worse off with headphones without noise-cancelation. That won’t happen with USB.
Third, power can be used to drive an amp in the headphone, which produces better sound quality. An example of such a headphone is the Mo-Fi. You can use it as a normal headphone, or you can turn the amp on, for better sound. But that again requires power. And if the Mo-Fi runs out of battery, the sound quality will reduce, which again won’t happen with USB-powered headphones.
Fourth, phones often struggle to drive audiophile-grade headphones to their maximum volume, while a digital connection can.
Fifth, Bluetooth headphones can come with a detachable USB-C cable, which you can plug into your phone to charge . And listen to music as it charges, if you want, with higher sound quality than Bluetooth, or if you must turn Bluetooth off in a plane.
Sixth, power can be used to drive a graphical equaliser that improves the sound, making up for the deficiencies of the hardware. This is not hypothetical. My Bose headphone has a graphical equaliser, and sounds much better with it on than off. The equaliser is powered by a battery, but USB power would be more convenient.
Seventh, high-end headphones sound noticeably worse when used with low-end devices, like an Android One phone, than with high-end ones like the Nexus 6 or Macbook Pro. With USB, high-quality headphones will always perform at their best, no matter what device they are plugged into. You won’t be forced to buy a high-end phone and high-end headphones for good sound.
Eighth, convenience — in my office, my desktop is under the table and off to the side, a few feet away, so my headphones’ cable is not long enough to reach it. But I have a USB hub right in front of me, into which I could have plugged the headphones.
Ninth, USB supports multichannel audio, say for use with a four-speaker system.
For all these reasons, headphones (and phones and computers) should all use USB-C.
Ideally, headphones would just come with a female type-C port. Since USB is an open standard, you can connect it to any port, by buying the appropriate cable. Like a C-to-C cable, for use with a newer device. Or a C-to-micro-USB cable, for use with an older Android phone. Or a C-to-A cable, for use with an older laptop or desktop. Or a C-to-Lightning cable, for use with an iDevice. All of these just work. No matter what port your device uses, your headphones will work with it.
There’s no reason to use the 3.5-mm jack any longer.