There's a few posts in this thread that one might find useful for mini-ITX even if the initial focus was on lower power setups with cpus integrated.
I'm interested in the Minisforum MS-01 system with 2 SFP+ ports and a free PCI-Express slot but they won't ship until April 20th or so. It would work well with an external 4-drive cage.
I was looking for what networking options I could use on my Legion Go that has 40 Gbps USB-C ports. So the timing of this thread was convenient.