When Intel first launched Skylake, one of the first changes we noticed was the uncoupling of the BCLK from other system clocks. Not surprisingly, this led to speculation that overclocking non-K chips using the BCLK would become possible. This eventually happened and many motherboard vendors started advertising the ability to OC non-K CPUs on their Z170 motherboards, allow chips like the i3 to be overclocked. Unfortunately, it looks like Intel is unhappy with this and is forcing motherboard vendors to issue a new BIOS update to remove the ability to overclock non-K chips.
Ever since Sandy Bridge, Intel has tied the BLCK with other clocks like the PCIe and DMI, limiting the ability to overclock as the other buses wouldn’t be able to hit higher speeds. This meant overclocks generally hovered about 3-5Mhz, minuscule compared to the 50% overclocks achieved using the FSB or even with Westmere. In order to access the ability to overclock, Intel made users purchase more expensive K-series CPUs which often had certain features disabled and enforced the use of pricier Z/Q series motherboards.
When Skylake came out with overclocking and heavy advertising support from motherboard vendors, many had hoped that Intel was changing its policies. It appears that motherboard vendors acted on their own though as they have quietly taken down any mention of Skylake overclocking on non-K chips. This is unfortunate for those who bought the Z170 motherboard with the promise of overclocking as they will not be unable to and their resell value has gone down.
For those who want to circumvent the new BIOS, older BIOS version with OC-enabled still exist for now. However, upgrading to the new BIOS may be irreversible so motherboards shipping from the factory now are probably locked down. New BIOS revisions may also feature bug fixes so there is also that to consider. Furthermore, if Intel wanted to, it could ask Microsoft to issue a Windows update to change the microcode of the CPU to disable overclocking. Given that the automatic nature of Windows 10 updates, that may be reason enough to hold off upgrading.