WebGPU doesn't have an rgb10a2 vertex format. It is required in all backend APIs:

• Metal: MTLVertexFormatUInt1010102Normalized
• D3D12: DXGI_FORMAT_R10G10B10A2_UNORM with "Input Assembler Vertex Buffer"
• Vulkan: VK_FORMAT_A2B10G10R10_UNORM_PACK32 with VK_FORMAT_FEATURE_VERTEX_BUFFER_BIT

It seem like an oversight that we never added it: #206 (comment)

Tentatively proposing milestone 1.