This is all still just rumor. The race to have products out the door on day 1 of a new iPhone launch means manufacturers actually chase these rumors and in some cases begin production of products before knowing if they'll even work!
The iPod touch is thinner than the 6/6S and it still has a headphone jack. Maybe Apple will remove it someday but there is no evidence that it will happen with the iPhone 7.
The iPod nano (5.4mm) is even thinner than the iPod touch (6.1mm). It still has a headphone jack.
And 5mm is the absolute minimum thickness for a 5-inch device; you really don't want a slab-shaped phone that is any thinner, otherwise the structural stress on it will genuinely make it warp/bend/crack in people's pockets.
Yes, it's still a rumor, but there's been enough independent corroboration that I think we can be reasonably confident it's actually happening this time.
Maybe they only want one port? Does that sound like Apple? Then they could add speakers on both sides of the port. Apple promotes music so having better audio would help them sell devices.
The iPod touch is thinner than the 6/6S and it still has a headphone jack. Maybe Apple will remove it someday but there is no evidence that it will happen with the iPhone 7.