Ditching the headphone jack? No way. Requiring powered headphones is one of the worst things they could ever do...
I agree. That would be a disaster for me. When I'm travelling it's frustrating enough making sure the iPhone has enough battery power when I need it. Forcing me to use Bluetooth headphones (a) drains power from my iPhone faster and (b) means I have another battery in my headphones that I also need to worry about.
I do think Apple will do something with the headphone socket though. They have a patent on a 3.5mm jack with the top approx 1/3rd cut off so that it is thinner. This would tally well with the rumours of them wanting to get the next iPhone down to 6mm thick.
I do still wonder whether another option just might be to use the lightning connector for analogue headphones. I know the current lighning connector doesn't have analog audio on any of the pins but isn't there smart circuitry in an Apple-approved lightning connector that can communicate with the iPhone the moment it's plugged in and negotiate what pins do what, currently primarily used to implement the reversibility of the connector I think. I wonder whether the communication protocols are expandable enough so that Apple could make a 3.5mm to lightning adaptor with the official Apple chip in it programmed so that, when it's plugged into an iPhone 7, it says "I'm a analogue audio device, please map ground, signal-Left and signal-Right to these three pins". I do see that the existing pins are very small however, maybe too small for decent analogue audio quality, but there is also a fairly big unused area of the flat bit between the current pins and the main body of the connector that could perhaps form a much bigger contact area suitable for analogue signals. There would still need to be negotiation on plug-in to ensure reversibility but it might be possible.
It seems worth the effort to me because relatively speaking the headphone socket takes up a lot of space internally and, if the iPhone 7 is going to get smaller, every little bit of extra space freed up for a bigger battery is like gold dust. I would happily pay an extra £10 or even more to buy the required 3.5mm to lightning analogue audio adaptor if the space saved by not having the headphone socket was given over to extra volume for the battery.