Tom's Hardware had the opportunity to visit Intel's overclocking lab and published an eight-pager about this experience, you can read it over here. The piece also contains some information about the future of overclocking. Specifically, Dan Ragland, the Principal Engineer of Performance Tuning & Overclocking Architecture at Intel, dispelled the notion that overclocking will become a thing of the past.
There's some speculation that overclocking headroom may disappear in the future but Intel is confident that it will not:
"It will not. Even when you talk 7nm and into the future, it will not," Ragland said with a certainty and finality that can't be conveyed with text, "What the other guys are experiencing limit-wise, we will not."
"I can tell you that, and feel confident in telling you that now: People who think this the end of the world for overclocking because our competitors' 7nm has very little headroom, that's not true."
When pressed for more details, Ragland admitted that the overclocking margin has decreased in recent years, but he believes this is a cycle:
"The decreasing margin is a concern," Ragland responded, "but if you look at this over the last 15 years, you have a cycle where you've got massive margin, and then that margin erodes, then you get more margin, and it erodes again. If we talk just CPU core, there are cycles where we've had a larger margin than others, and it's true that you get paid more for POR (i.e., stock) performance more than overclocking performance, so that tends to win."