Based on your argument, I can see why you'd think this. Your argument is one that I would expect from an audiophile, but not a full time musician. The lack of an option to mix on headphones, is unacceptable to many musician, ESPECIALLY these days.
When you're in a profession studio and see a producer come in for a session and place his Macbook on a mixing board, for a quick session and then leave, you'll get it. Most musicians work on the go, when working in the studio isn't an option, for whatever reason. Nobody wants to carry around interfaces.
I'm not trying to argue a point due to my desire for a headphone jack. It's simply how it is. As a full time musician, it's my experience that colleagues and other fellow musician acquaintances are increasingly producing on the go. That's why I know you can take a headphone jack out of any other Mac product, except the MBP line.
I have to agree. I do a lot of on the go stuff. I might be stuck in an airport or riding a commuter train and decide to put together a quick sketch of a composition.
Likewise a lot of people working in news/video/post/film may put together rough edits or just comb over raw footage while on a flight or in a hotel room.
Lots of pros carry their laptops with them all the time, without any kind of audio interface. All of that stuff is packed with the gear, or back at the studio.
When we are doing this we are often wearing ATM50s or MDR7506's. Big old closed back headphones with 1/8th" plugs.
Not bloody little wireless ear buds.
I really hope the next MBP does have TB3 on a mini DP connector, a regular headphone jack and a decent amount of power to able to do video production work.
I some how doubt I will get an actual professional machine. Instead it will be the latest victim of Apple-anorexia.
Part of me is okay with that. Like many other people who have thrown in the towel, I'll switch over to Windows and Linux. Lots of people are doing professional audio and video production on Windows. It's ugly, and you have to really mind your security, but you get all the jacks you need.