If more cores were unlocked, intel would simply decrease the stock frequency and vcore to keep cpu in same power/thermal envelope 130-140W. They do this with server cpus with higher cores.
Even the 5960X 8 core cpu is 3.3 max turbo at stock. The 3 others with fewer cores go up to 3.8/4 max turbo. More cores = lower stock frequency/lower stock vid to maintain power/thermal envelope.
All 4 may well overclock the same, then the extra power of one with most cores is the end users cooling problem, as intel only has to worry about stock and that is easily maintained by altering mhz/vcore. Which is why sometimes enthusiast cpus dont come with a cooling solution as once overclocked they require water, or at least high end air, hence the stock cooler is wasted money.