Should totally work with anything PCIe, not only GPUs. When I just got a Thurnderbolt 3 eGPU box, I tried storage and network controllers in it and they all worked. Since this is just raw PCIe, other cards should do too here.
Although I remember seeing somewhere that the particular board with the PCIe connector that I use might have not routed the 3.3V rail from the power supply connector to the PCIe connector, so even though 3.3V is required by PCIe spec, it’s missing and the cards that require it will not work. Can be solved by using a better adapter, though