All the 5xxx cards have displayport. They simply adapted the standard.
Highly unlikely they adapt to Mac Pro customers when we are probably below 0.1% of the total market.
That's true however, if Apple does choose to offer it in their next upgrade or even as an upgrade to older Mac Pros many people would run to buy one, including me.
The 4870 is ok but only a company like Apple can get away with selling it at 450$. It's about time they begin offering us not OK but great graphics cards like the ATI 5970 or GTX 380,
which is expected in Q1 of 2010. I think it would be highly profitable for
to offer this card as it packs a whole bunch of power and remains under their 300W limit for PCI-express slots along with the fact that they
wouldn't have to pay ATI extra money to incorporate MDP as they wouldhave to with NVIDIA.
I know that if Apple would offer it I'd run to buy one as I am sure many others would.