The market for Blackwell 6000 Pro or something similar is a LOT bigger. Dont forget that servers and workstations are connected each other with similar technology and yet, Apple is killing their own market.
Besides, Apple's GPU performance isn't great so what's the problem with that? Apple dont even have RTX 5090 grade GPU and workstations.
Servers don’t run on RTX cards. And Apple doesn’t sell servers. They might build some for their internal use, and that can take whatever shape as suits their business needs.
So far you seem to talk about ML workstations and servers as if they were the same thing, which is not correct. I fully agree with you that Apple would benefit from shipping faster and more capable GPUs. I don’t see however how this translates to them needing a Mac Pro or pluggable GPUs. IMO, pending some advances in GPU tech, an Mx Ultra Studio could be a competitive ML workstation, and a cluster of two such Studios would still considerably more cost-effective than a hypothetical Extreme chip. I too would like to see a nice modular Mac Pro with pluggable computer boards, but the reality increasingly looks like there simply isn’t enough market demand to absorb the tremendous R&D and manufacturing cost.