This article did not surprise me at all. Like many people in this thread, I've been having the "mysteriously shut off at 30% with no warning" problem with my iPhone 6 for going on a year. In my case, it seems to particularly occur when (a) I'm using the GPS (while running) and sometimes other apps such as music and (b) the ambient temperature is below about 55 degrees Fahrenheit or so. (Yes, I know the phone is designed to shut down below freezing - this is not that. I live in Atlanta so we don't get below freezing temperatures that often).
Like the others in the thread, I've had Apple techs repeatedly tell me the diagnostics on my phone reported nothing unusual about my battery. However, I stuck with it and kept opening new cases. I also kept a detailed log of the temperature, the battery percentages, and other exact details of incidents which did occur so I could relay the details.
Finally, on the third tech case, I got it escalated up the line and the higher-level tech granted me an special exception. Apple swapped out my battery, for free, even though my iPhone 6's AppleCare had expired (last September) and therefore I was WELL out of warranty.
Other than waiting for this battery exchange program to materialize, I would recommend being persistent with Apple Support and give them as many details as you can. In particular:
(1) Set your phone so you see battery percentage on the status line, and keep track of what numbers you see when incidents occur. That makes your report more concrete.
(2) At least once, do TRY the recommended procedure of "Restore your iPhone, iPad or iPod touch to factory settings" that the online support help recommends. (Of course, back up your device and restore from backup after the reset). I know its a pain to do this, but it overcomes a hurdle with front line support techs - you can honestly tell them that yes, you did that, and it did not help.
(3) Keep being friendly, honest and persistent with the Support techs, and ask to be escalated if need be.
They ended up swapping out my phone at my local Apple Store, and I've had no issues since then. There is light at the end of the tunnel.