LeEco's latest smartphones and the new Moto Z all ditched the 3.5mm jack in favour of USB-C only.
Apple also figured now is a good time to do it and had a good hardware design reason to do it.
People that have 3.5mm jack only hardware can keep using their current phones, no one is making them buy the iPhone 7 and even if they do, because it comes with the adapter they'll still be able to continue using card readers and such.
As with all technology being phased out in a certain field, at some point people will have to refresh their peripherals. Backwards compatibility that compromises their design and vision is usually not something Apple has ever been concerned: they'll maybe give you workarounds (adapter) or sell you one.
Personally I was hoping they would also just go for USB-C on everything, but guess they need to justify their investment on the Lightning port's development and keep control over its function.
Charge and listen to music on headphones? You are doing it "wrong". Not wrong, just "Apple wrong" - never did it, but can see how a lot of people do at the end of the day commuting home.
Clearly Apple wants to push everyone wireless, which kind of makes sense if you buy into their ecosystem and vision (Macbook, iPad, iPhone, iWatch), since it allows you to switch device without unplugging anything, but also, in this case, those wireless earphones might (pure speculation here) be the embryo of their "Google Glasses", something they can now build upon and experiment.
EDIT: Just came across a 2010 video of Steve Jobs pretty much summing up what I tried to convey, which is Apple is just being Apple and shows coherence with what happened with the 3.5mm jack: https://www.youtube.com/watch?v=65_PmYipnpk