Regarding socketable memory - I believe that their current memory setup is significantly faster than any system with socketed memory. Given that they market the memory bandwidth heavily in their specs I imagine this would lead to a perceived performance drop for what is essentially their most expensive system.
My one gripe with the new pro is that they have reintroduced a problem they themselves solved, because they chose to not support discrete GPUs. MPX looks like a really neat solution to both internal system cable management, and the routing of thunderbolt and display data through the system. It's a shame it only existed in one generation of one product
Interestingly enough from looking at pictures of the new system board - they have less power cable connectors than the 2019. Is the new system using a smaller capacity PSU than the old?
The Mac Pro is Apple saying: “if you need more than 192GB of RAM, we can’t help. But if you need PCI-E, we have a lot of old Mac Pro enclosures left over from the past 3 years when we didn’t sell any Intel Mac Pros, here’s a Mac Studio in a bigger box, enjoy”