At SIGGRAPH 2016, the Khronos Group revealed they're working on the core specification of Vulkan Next. This next-generation API is in active development and the Khronos Group said some features may come out as extensions.
Key priorities for Vulkan Next include better multi-GPU support, new features for VR, cross-API and cross-process sharing, subgroup instructions, generalized renderpass/subpass dependencies, and a rigorous memory model.
The scope of the improved multi-GPU support wasn't sketched out so it's probably not worth speculating about right now. In the presentation it was just said the current multi-GPU support wasn't very polished so it would be improved. The VR support will come by way of more efficient multi-view rendering, direct screen access and other tweaks. These techniques are useful in optimising content for VR headset displays like the Oculus Rift and HTC Vive.