Here’s a Kickstarter project to solve the problem of no audio jack which illustrates just how thorny it is: iLDOCK – charge and listen to iPhone 7 at the same time by ildockgear — Kickstarter.
ILDOCK lets you use your wired headphone while charging your iPhone 7. You can also add storage via SD, TF and USB ports with Plus.
The problem, as some have highlighted in the comments, is that Apple rarely grants MFi status to accessories where the lightning cable doesn’t plug directly into an Apple device. In this case, one does but the external one doesn’t. Most manufacturers get around this by making the external one a microusb. I don’t mind that, in fact it helps me, but some folk aren’t crazy about it.
There are other issues too, of course: if you have lightning headphones and want to charge, this isn’t going to help you.
I know I’ve written before that the future is wireless, but this project, worthy though it is, merely illustrates how ugly the interim is going to look like.