FWIW, the earphones on my iPhone 6 (week 36 production, purchased via pre-order on Sept 19) have a very snug fit, with no reason to believe there is any travel or loose connection; however, I still experience the issues of random pauses/skips and Siri/voice activation, and it does seem to be getting worse by the day.
Judging by the behaviour, I believe this does indeed have something to do with the metal contact at the base of the jack. BTW, I'm using a pair of (excellent) RBH EP2 earphones. There is in fact a note on RBH's website indicating they are "aware of the Apple problem", and that a change in housing design on the iPhone 6 has resulted in undesired operation with the earphone's control functionality. After contacting a company rep at RBH, I was informed that they are conducting their own investigation with an iPhone 6, and will send a replacement or repair kit as soon as one becomes available - excellent customer service in my opinion!
For those who have received a replacement iPhone at an Apple Store, something tells me that your new phone *may* be at risk of developing the problem again. I only mention this because I don't recall having this issue in the "early days" of iPhone 6 ownership. The problem began occurring (for me at least) only a few weeks ago, and has become progressively worse.