Maybe they are just for internal use? I doubt Apple is going back on the server market, and given how little they have invested in the Mac Pro, I doubt they are going to make a new version. There is little advantage compared to the Mac Studio for most users. External GPU support would change that, but it doesn't seem to be what they want.

Expandable machines are attractive when the future is uncertain. I imagine a server chip would have abundant DDR6 and PCIe lanes. Oddly enough I’m now buying my PCs with all memory slots occupied because of bandwidth. I can still change the sticks for higher capacity, but expansion is a lot less convenient than when memory bandwidth wasn’t something more desirable than raw CPU performance.

I’m not sure if I can measure IPC and cache misse latencies on my machines, but I’m sure latencies are pushing IPC down.