hardCOREware speculates base clock overclocking (BClk) may return with the introduction of Intel's Haswell processor later this year. Base clock overclocking was severely limited with the introduction of Intel's Nehalem architecture, but it seems Haswell may reverse this because of Intel's focus on power efficiency:
Intel immediately discovered a design flaw in tying the L3 and CPU speeds together – if the GPU ever needed to access the L3 cache, the CPU speed would have to wake up as well. With Intel’s focus on power efficiency, this was a huge deal, which is why they will actually go back to individual clock speeds for the Uncore and CPU Core with Haswell.
This is pure speculation on my part, but it looks like the days of overclocking a locked CPU may be upon us again. By being able to manipulate the Uncore frequency separately from the CPU (and GPU) frequencies, there is a good chance that the lower end Haswell chips will become viable overclocking targets for enthusiasts once again. We may never see another 300a, but if we can have a $100 Haswell CPU running at similar frequencies to the $300 part, it will renew interest in overclocking for a lot of people.