Officially, Haswell overclocking requires two things: one, a K-series variant of the processor, and two, a motherboard with a Z87 chipset. Several motherboard makers have recently circumvented the second requirement, enabling Haswell overclocking on H87, B85, and H81 mobos via a firmware update. Unfortunately, it looks like that workaround may not be available for much longer. The folks at Hardware.fr asked Intel about the workaround last week, and they received the following statement.
Intel plans to release a microcode update that limits processor core overclocking to Intel Z87 based platforms WW30'13.
"WW30'13" seems to be shorthand for week 30 of this year, which is this week. It's not clear how quickly the update will be rolled out in the form of firmware updates for motherboards, but I assume we'll eventually see Haswell processors with the new microcode trickle into e-tail stocks.
In other words, if you're planning to build an overclockable Haswell system, you're probably better off going the Z87 route. It's possible that motherboard vendors will find another workaround to the limitation, but I wouldn't bet any money on it.