This is a feature request to support HW clip planes. It is OK for a platform to return that it support 0 HW-clip planes.

Each of the "new" 3D API's have HW-clip plane support (atleast a cursory look supports this):

1. Vulkan: VkPhysicalDeviceFeatures has fields for both clipping and culling (shaderClipDistance and shaderCullDistance) along with how many from the fields maxClipDistances and maxCulldistances from VkPhysicalDeviceLimits

2. Direct3D12: see the enumeration D3D12_CLIP_OR_CULL_DISTANCE_COUNT at https://docs.microsoft.com/en-us/windows/win32/direct3d12/constants

3. Metal: see 5.2.3.3 Vertex Function Output Attributes of the Metal 2.2 shading spec,
   https://developer.apple.com/metal/Metal-Shading-Language-Specification.pdf.

I am just advocating for clip-disance and not cull-distance as the latter is more esoteric IMO.

I advocate that this feature to be part of the 1.0 core interface and not as an extension.