"... Thunderbolt is great for peripherals, but as a semi-permanent interconnect, I have worries over the port's physical stability ..."

Thunderbolt as a server interconnect displeases me aesthetically but my conclusion is the opposite of yours:

If the systems are locked into place as servers in a rack the movements and stresses on the cable are much lower than when it is used as a peripheral interconnect for a desktop or laptop, yes ?

This is a semi-solved problem e.g. https://www.sonnetstore.com/products/thunderlok-a

Apple’s chassis do not support it. But conceptually that’s not a Thunderbolt problem, it’s an Apple problem. You could probably drill into the Mac Studio chassis to create mount points.