My take: It is part of a tethered pro system
A Mac mini, with its relatively limited graphics power, doesn’t seem well-suited…
The Mac Mini houses upgradeable memory and a good fast drive. Then it links to an external GPU box that can be configured however the pro wants it, and is upgradeable.
And external box containing multiple drives for a RAID (upgradeable of course). all attached to a 5K monitor.
So it becomes just like a stereo separates system but with Thunderbolt connections. Because Thunderbolt 3 is fast enough.
Then they can update the mini every so often without needing to redo graphics and storage. Same for other peripherals.
Image: Jan Hammershaug