due to intels pricing model and artificial deliberate market segmentation and lack of competition, intel will not produce dual processor boards for i3/i5/i7 chips, though this be fully within the realm of possibility. This is so they can reserve the concept of 8 – 12 core machines for server level only, if they wanted intel could produce a dual processor i5 2600k, which could then evidentially be clocked at 5ghz yielding 40ghz in a single box/machine very usefull for render farms and those who currently need as much power as they can get, there is no reason apart from pricing models why this machine could not be built for under a grand, but technology companys want to make as much money as possible, so they drip feed change into the market at their own pace, because amd and intel together are not providing enough market competition to make such a machine possible, it would be more likely for amd to offer a cheap 12 core system than intel if it were to happen. though its probably possible to build a dual processor opteron system cheaper, once you look into pricing a dual processor xeon or opteron system you begin to realise a mac pro though expensive is a reasonably priced system compared to doing it yourself.
it would currently and probably for the near future be more cost effective when building a render farm to buy quad i5 2600k’s and overclock them to 5ghz or single 6 core phenom systems, than buy or build any 8 or 12 core systems, purely from a pounds per gigahertz render-farm perspective.