The hot plug and power management stuff referred, I believe, to the driver, and I will definitely have to address those issues, which might present a challenge.
The x4 electrical and PCIe 2.0 issues I thought the HP comparison shed some light, if only an existence proof.
I have also tried a pre-production Intel card with 2 10Gig ports, 4 1G ethernet devices (although with no external connectors) and a honking big crypto accelerator. This shows up in the Sonnet, although all the device IDs looked suss, but it did manage to negotiate links to the various devices.