Note that we don't know there isn't a CrossFire bridge. These cards aren't in any standard form factor. The connectors at the bottom could have additional pins for this as well as standard PCIe.
they also have to run the DisplayPort outputs through this bottom connector. PCI-e SSD connectdion ... again through this connector.
that doesn't seem to leave copious spare room for Crossfire pins as well. The connector already has 3 functions already. Adding 4th is just complexity that just isn't needed.
I admit it's unlikely Apple would bother for a feature OS X doesn't support, but it can't be ruled out. Maybe they're planning to support it in some way in the future,
Doubtful in the future. More likely Apple is going to have another design bake off and there may be a Nvidia GPUs in the next card. I highly doubt Apple wants to sink engineering resources into keeping both of those proprietary solutions going forward.
"Crossfire"/"SLI" over standard PCI-e i can see Apple getting behind but not these proprietary, vendor lock-in, sockets. Apple is far more likely going to want situations where they make the vendors compete and pick whatever winner best meets their criteria on each iteration.
or maybe they just see good performance in Windows games as a nice perk for pros who want to unwind at the end of the day or whatever.
If there are AMD drivers that work over PCI-e v3 fine. But I suspect that these are going to be signficantly far out of the Windows gaming market mainstream. ( AMD has had "Crossfire over PCI-e drivers" before that didn't go very far. )
Do we know that Tahiti not doing CrossFire over PCIe is actually a GPU limitation, or is CrossFire implemented by other components on the board? If the latter, Apple could have done basically anything here.
The critical issue is pathway to/from Memory to the PCI-e bus. So the GPU is the primary piece involved here as to whether the performance is "just as good as" the other solution over the proprietary slots.
