Again, most of your better quality headphones will have removable cords. If you want to hook up to a laptop/desktop that only has USB-A ports then you hook up the USB-A cable. If you want to use with an iPhone/iPad you hook up the lightning cable. If you want to hook up to an Android device you hook up the Micro USB or USB-C cable. If you want to hook up to a legacy device you hook up to the 3.5mm cable.
I think the only difference may be Beats headphones might have a lightning port on them, where other companies will probably have a USB-C port on them.
There will probably be some headphones without removable cords that only have a built in lightning connector (most likely the EarPods that come with the iPhone). Those will be good enough for people that only use the headphones with their phone/iPad. There will be a ton of companies that start making cheap ones like this that you will find in most gas stations, supermarket checkout lines, etc right along with the phone chargers and lightning cables for when you are on a trip and your other ones get lost/broken.
I think beats will have one USBc and one Lightning, in the same way some Beats have two 3.5mm adapters. In this way, Beats is universally compatible with USBc equipment (including their own Macs), but also offers a pass through for charging, or friends daisy-chaining off your connection. I'm also expecting them to add a Lightning port to the Macs, so rather than male-to-male Lightning cables, the same USBc-to-Lightning cable used to charge the phone, can be used for the headphones as well (and also the MacBook). And having just one cable to carry around will greatly simplify traveling for most.
But otherwise you pretty much hit he nail on the head.
I also see removable third party hybrid cables for headphones that have several connectors on the end of the cable to address the needs of those who switch between different devices all day long, which solves the problem of keeping track of several different adapters. This is a problem that has come up over and over on these boards, but I find it hard to believe it represents the habits of the majority of headphone users. Most I have seen have one set of headphones that they use with one device on a regular basis, so customers will simply buy the cable that best addresses their needs.
Of course I'm looking forward to BT 5 and whatever other wireless improvements Apple has been working on, because I'm all for cutting the cable, even if it's one more thing I have to charge. And I fully expect Beats wireless headphones to have the same ports so that if I do run out of power, I can plug them into whatever I need to in order to keep listening.
I think what most of the detractors here are overlooking is the reality that audio is going wireless, and most if not all, would prefer that to being tethered by a wire, all things being equal. So as customers increasingly turn wireless, the fallback to cables will be strictly as backup for when the current battery tech fails to last as long as one needs. So cables in the future don't necessarily have to be as easy to use as the 3.5mm Jack has been. But obviously there's no reason they can't be.