Are there any plans to implement these extensions?
Draw parameters appears to be working when running without validation, so did someone just forget to expose the extension?
vkGetPhysicalDeviceFormatProperties doesn't report vertex buffer support for VK_FORMAT_R16G16B16A16_USCALED (and other _USCALED formats), but when running without validation this is working just fine. Is the lack of capability misreported or is it not supposed to be supported?
Support for all three extensions will be released at some point in the future.
As for the vertex buffer support for the rgba16_uscaled and related formats, if your application assumes these formats to be supported even though the driver says otherwise, you are entering an undefined behavior's land. Even if it works on your ASIC, it does not have to be the case on other models.