The two extensions include VK_EXT_hdr_metadata and VK_GOOGLE_display_timing.
VK_EXT_hdr_metadata is a renaming of the VK_EXT_SMPTE2086_metadata extension, which supports SMPTE 2086 meta-data in the swapchain. The new extension furthers this by also including CTA 861.3 meta-data support, which improves Vulkan's HDR support.
VK_GOOGLE_display_timing allows applications using VK_KHR_swapchain to retrieve information about the presentation engine's display, obtain timing information about each present, and to schedule a present to happen no earlier than a desired time. Developers can use this to minimize stuttering and other anomalies.