I don't see who the target market is the iMac Pro. Pros want easy user upgrade ability. For $4,999 it should be easily user gradable. It doesn't even have panel to access the memory.
Pros who do their own support want that.
Larger operations would have dedicated staff and loaner machines to handle such work as they would be certified and authorized by Apple to perform the work and would have the spares on hand.
My friend works in Nike's IT department and they are a large Mac installation and they don't take the machines down to the Genius Bar when they have an issue.