Marco Arment has a few good ideas of what the next Mac Pro might entail, including concerns that there won’t be another Mac Pro. I take issue with this paragraph, however:
One big question is Retina-display support. If Retina displays are coming to the MacBook Pro soon, would they spread to the rest of the Mac line within a year or two? If so, wouldn’t the next Mac Pro generation need to support them, presumably with the release of a Retina Thunderbolt Display? That’s a big requirement alone, and it would also require special video cards that could drive two or three of them. (The sheer amount of manufactured pixels and GPU throughput required to pull that off makes me think that Retina Thunderbolt Displays might not exist for a while.)
Keeping in mind that we are speculating from a very distant point about Retina Macs, Arment’s concerns may be ill-founded. As John Brownlee explained, Retina displays are closer in Macs than we’ve otherwise thought, as they don’t necessarily need to double in resolution. He notes that the current resolution of the 27-inch panel in the current iMac and Thunderbolt Display is 89% of what, mathematically, constitutes a “Retina display”. He did the math, and worked out that a display of 3840 x 2160 pixels is 133% of a Retina display, which any Mac Pro can comfortably output.