This might be a reality on the next machine. To properly get TB working there might need to be an integrated GPU apart from any optional GPU cards.
That hardly gets you a Mac Pro with no GPU. Just no GPU PCI-e card (all PCI-e slots open). But yes that should be sold more inexpensively than one with the nominal "entry" (really mid range) level GPU card in it.
I don't think that would be the default configuration though. I think two GPUs would be standard config and this could be a BTO option. ( It probably would be the default config for the "server" version though. It is a question if they'll let it be a mainstream BTO option).
One question with an embedded GPU (required by TB ) would be though whether matching the other embedded GPUs (MBP 15" and iMac ) would force a clean sweep of vendors for the default configs ? Or would Apple be willing to go something like a 7xxx card and 8xxxM embedded GPU for the Mac Pro even though that doesn't maximize part reuse for the embedded GPU ?
I'm sure someone will complain if they had one from each vendor .... since that would negate one vendor being selected over another.
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Sandy and Ivy bridge both have integrated Intel HD video.
Actually they don't. The microarchiturecture is independent of package die integration specifications. Xeon E5 class SB and IB don't have any HD video.
And it saves money for the GPU-centric users to pick whatever card we like.
If Thunderbolt is a high priority though that may drive an embedded GPU onto the motherboard. There is no material system difference in that context. [ Whether the CPU and GPU are all in one single package is immaterial to the system design. ]
Folks could pick whatever
second (or third ... ) GPU they wanted, but they'd still be taking at least one driven by Apple's system specifications.
In the single CPU package set up variant of the Mac Pro, the system probably would loose a x16 slot to at best being a x8 slot (or worst disappear ). There is still an open x16 slot so folks can choose the card that want that fits the power allocation.