There was some talk and rumors regarding HD 6790 unlockability in the weeks prior to the launch, but now, when the card is launched and reviews are out there is still no confirmation that the HD 6790 can be unlocked.
The story is quite simple as the HD 6790 is based on the same Barts GPU as its HD 6800 series brethren, it simply makes sense that these card could be unlocked. Some partners based their own design on the HD 6870 PCB, thus giving the HD 6790 two PCI-Express 6-pin power connectors and HD 6790 is also a decent overclocker as it can pretty easily reach the 1GHz clock for the GPU. Of course, we are talking about overclocking potential of the non-reference cards and not the AMD reference design.
The other side of the story is that AMD might have implemented more serious measures in order to keep the HD 6790 below the HD 6800 series, so it wouldn't interfere with the sales of the latter. AMD definitely learned a thing or two from the HD 6950 launch as during that time the unlockability of the HD 6950 to HD 6970 was almost 100 percent (and might still be) and it simply made no sense to go for the HD 6970, at least for those that were familiar with simple BIOS flashing.
We are still waiting for even some hint of HD 6790 unlockability as this would make this card really interesting and not just another US $150 mid-range card.