Hacker News Reader

Do you know about the Minisforum B550?

It has an external PCI-E 16x male port that goes into a small dock/riser where you can plug a graphics card for instance.

https://droix.co.uk/blogs/minisforum-b550-review/

A second review with a different conclusion: https://www.youtube.com/watch?v=ihcGnBjUAm4

Not so reasonably priced, so it maybe does not fit your criteria.

You can get flexible risers to turn the m.2 slot into a PCI-e 4x

Intel has the NUC Extremes which offer a full x16 slot in a fairly small footprint. The Core of the computer itself looks like a small GPU, and it plugs into a daughter board that acts as a coupler for its two x16 slots.

I think most people throw GPU's in them but I don't see a reason why you couldn't just fit it with a nice NIC

Have you heard of zima board?

https://www.zimaboard.com/

Zimaboard has a PCIe external expansion, 2 external SATA ports, and 2 NICs. Low power, passively cooled.

Too bad it is using a CPU from 2016. At that point its competing with substantially better used hardware that is less expensive.