None of the Apple Silicon hardware can seemingly justify this form factor, though. The memory isn't serviceable, PCIe devices aren't really supported, the PSU doesn't need much space, and the cooling can be handled with mobile-tier hardware. Apple's migration path is "my way or the highway" for Mac Pro owners.

The most notable feature was that there were mac-specific graphics cards, and you could also run PC graphics cards (without a nice boot screen). They had a 1.4kw power supply I believe, and there was extra pcie power for higher-end graphics cards. You could upgrade the memory, add up to 6 or more sata hard disks (2 in dvd slot). You could run windows, dual booting if you wanted and apple supported the drivers.

The 2013 was kind of a joke. small and quiet, but expansion was minimal.

2019 looked beefy, but the expansion was more like a cash register for apple, not really democratic. There were 3rd party sata hard disk solutions,

the 2023 model was basically a joke. I think maybe the pcie slots were ok for nvme cards, not a lot else (unless apple made it).

nowadays an apple computer is more like an iphone - apple would prefer if everything was welded shut.