I don't know whether the disabled cache will still consume power.
You lot all assume that the unlock is stored on the hard drive but that might not be the case. It could be in the BIOS or even on the CPU itself: there could be a fuse which is blown when the correct code is executed, like on a old fashioned PROM, which I hope is the case.
I hope the idea will prove unpopular but I don't suppose that would stop them, if people won't buy the upgrade or the crippled CPUs, they'll still sell them anyway and perform upgrades before they're sold in the factory, as needs be. In a way, I hope they do sell crippled CPUs but a crack gets developed and most consumers are using it within a month so they don't sell many upgrades.