The Vulkan specification (with extensions) does support multi-GPU and multiple video output. However, I've never seen any demo showing this feature.

Can someone confirm whether that's supported with an Nvidia Geforce card? If not, what about the support from AMD Radeon?

To be precise, I'm looking at a game-like application that would use two graphics cards and two LCD monitors, one monitor connected to each card. The idea is to connect two HMDs to the same game, each HMD having its full GPU (both for rendering and video output).

Please note that I'm not interested in connected two DisplayPort to the same GPU because that means the final frame buffer of the second card would have to be copied over PCI-Express to output on the first card. At 4K resolution, that's a significant performance hit. So I would need each card to do their own video output over DisplayPort.

Is this supported somehow on Geforce and/or Radeon?
If not, maybe it is on Quadro and/or FirePro?