You can't put 2 Core i7s on a server mobo; Core i7s only have 1 QPI link. You're looking at Nehalem-EPs or EX, and those are Xeons, not Cores.
And if you're looking at a server/workstation mobo, you can get anywhere between 4-9 slots of memory per socket, not just 6. Although you'll need ECC memory for that, so forget about your typical epeen-desktop budget.
Show me someone who puts Windows 7 Home on his/her server mobo, and I'll show you an idiot. W7H RAM limit should not be an issue.
P.S. and by the way, that setup you envision isn't complete without a Quadro FX and/or a complement of Teslas. Geforce? Nobody of sound mind wastes a setup like that on just gaming (unless you're using those Geforces as budget CUDA compute cards).
You way underestimate what the Enthusiast consumer will do.. I mean these are people that will pay $500+ for a Video card. Buy those insanely priced new CPU releases that can go up to $1,000, etc. Buying a $500 motherboard wouldn't mean anything to them if they wanted it.
I should've clarified; I meant that nobody would install Windows 7
Home on a server/workstation (and hence run into the RAM limit). If they can afford a $500 motherboard and the corresponding processor, they should easily be able to afford an appropriate OS version.