Experts said a year ago the technology wasn't ready for larger screens, let alone the unfathomable volume and spec that Apple requires. No such claims were made about 64-bit processing, and the two aren't analogous. There's absolutely zero chance we'll see this in the 6S. Even a switch to more traditional OLED seems unlikely.
I suspect this technology will be like Liquidmetal. It'll get speculated every year, but rumors are pretty much always unsubstantiated.
A year prior to the release of the 64-bit A7 no one was even talking about it, so that's not really a good example to compare this too. On top of that, "experts" -- if you can even call them that -- are frequently wrong. A year is a long time in tech and a lot of advancements and improvements can be made in that time.
While mLED isn't very likely to be in the 6s, the chance of it having an OLED display is definitely there. I'd even say the chances of it having an OLED display are quite high. They're already using OLED in the Watch so why not move it to the iPhone as well. They're already taking Force Touch from the Watch and bringing it to the phone so bringing over OLED wouldn't be surprising either.