Farewell, Skylake BCLK overclocking, we hardly knew ye. ASRock has pulled the plug on its SkyOC feature, not even a couple months after it appeared in motherboards' firmware. The latest BIOS updates for some of the company's Z170 motherboards explicitly confirm that ASRock is removing the feature from its firmware. The beta BIOSes that included SkyOC in the first place have been scrubbed from the company's site, along with the announcement page for the feature.
A while ago, WCCFtech noticed some rumors that Intel was about to roll out new firmware updates to disable base clock overclocking support on non-K CPUs from the Skylake family. The company apparently didn't like the idea of users grabbing inexpensive versions of Core i3 and i5 chips and pushing them close to Core i7-levels of performance, and now those restrictions have come to pass.
This is roughly the same scenario as what happened back in the Haswell days, when Intel dropped support for limited multiplier overclocking on non-K chips from that family. Of course, users are still free to use an older version of their motherboard's BIOS and keep BCLK overclocking active, but they'll be missing out on bug fixes and feature updates.