The Wifi vs Ethernet comparison is really not the same. How are Bluetooth headphones more convenient than standard headphones? It's one more device you have to worry about pairing and charging. With Apple removing this jack, only the new standard would be able to be used--you wouldn't be able to use wired headphones at all.
Look at game consoles or actual pro desktops. Ethernet ports are still on them, and they also have Wifi cards to use a wireless connection. They didn't get rid of Ethernet because Wifi was newer. Just like if Apple wants to remove this jack--why? Instead, why not ship the iPhone with lightning or BT headphones and use that as your standard but still keep the jack for those of us that use or prefer wired headphones.
It's exactly the same. You're skating to where the puck is, and not where the puck will be. Forget where Bluetooth technology is currently, and imagine where it will be in the future, especially if that future is driven by necessity to replace the 3.5mm jack. All of your complaints will get better, and eventually nonexistent The bottom line is that the future of audio is wireless. All things being equal, would you rather be tethered to your equipment with a wire, or have the freedom to go anywhere?
And how exactly will you not be able to use a wired headphone at all? There will still be a Lightning jack, and with an inexpensive inline adapter, of course you can use any headphone you want.
My MacBook Pro no longer has an Ethernet connector, I have to use an adapter. And neither does my Roku box. My iPad and iPhone don't have Ethernet connectors, and I don't even have the option to use an adapter with them. So no, not all devices have the option for both Wifi and Ethernet, and the list that does is dwindling every year. Besides, desktops and gaming consoles are fixed devices. It's not even the same use case as a mobile device, which is what the essence of a headphone is.
And why can't they have both? Because in part what's motivating them to remove it at this juncture is to free up over 184 cubic mm of internal space presently occupied by the redundant 3.5mm single purpose jack. That's a huge amount of space in a device as constrained as the iPhone, which could be better used for new technologies, or a larger battery, without having to make the phone any bigger, all of which keeps them competitive with Android, and Samsung.