Except for every other time in history when people do change when they still have the old. No one stopped making 8-track, cassette, or VHS players when the new standard to replace them was first introduced. How many of us had stereos with a cassette player on the front and a CD tray on top? Or VCR/DVD combo? You transition. You integrate. You don't replace out of the blue. Totally taking away the old standard in a single generation is not the way advancement usually happens. That's the Apple philosophy of "you need what we say you need". Everyone else continues to support the old standard. If the new one is actually better, it will take over on its own.
Whether or not it is a vocal "minority" that is opposed to the loss of the headphone jack remains to be seen. I really think that some people here are underestimating how much this matters to a lot of people. A standard headphone jack is one of the most ubiquitous features in modern technology. You're right that there would still be complaints if they removed it a year from now, but a lot more people will have gotten used to the new headphones packed in the box, and there would be a lot more 3rd party options. There's really no rush to get rid of it at all. Having access to a floppy disk drive didn't stop people from adopting new storage technology that offered clear advantages.
It's also not really fair to say that it's not like everyone is being forced to adapt, because everyone who wants a new iPhone this year is. Anyone who wants or needs a new flagship phone this year either has to give up the jack or switch platforms.