As promised, I checked the possibility of modifying the Unleashed D200+ to make it fit the D800:
It is possible to get it to work, but you have to remove A LOT of the casing, and actually you would even need to remove some of the PCB (see how it sticks out of the cut case), which will quickly cause great problems if you overdo this.
(yes, that extra cut out is for the new „3D“ white dot)
While some brave souls will attempt to do this and will probably manage, This is not a solution I will recommend to our customers.
Forum thread showing the modification
We’re working hard on a successor to the Unleashed D200+, and are redesigning it to make sure it fits the D800 properly. We will make existing customers some sort of an upgrade offer, be it trade in, or just a loyalty rebate of some sort, we still need to work out the details on that. So don’t hesitate to get the Unleashed D200+ for your current camera, while you’re saving up for that D800 – you’ll be able to upgrade the Unleashed as soon as we have the new version ready.
Sorry… I wish I had better news than this.