I had the same thought during the SIGGRAPH presentation. The API they are providing is a step back, too high-level, like going from Vulkan back to OpenGL.
It is nice to have for starters, but in the near future it will die quickly if somebody comes up with an improved incompatible technique, that can be implemented over existing low-level.
Who is they? NVIDIA provides multiple APIs which are accessible through various APIs or natively the point of the hardware is to provide specific interfaces and data types which make RT faster these are not limited to a specific graphical API.
You can use it trough Optix which is proprietary low level C++ API based on CUDA, you can use it with Vulkan or DX12 DXR the levels of abstraction are dependent on what API/interface you’ll be using.
On top of that NVIDIA provides ready to use hybrid ray tracing libraries which are built on top of Microsoft DXR currently with Vulkan coming within the next 2-3 months.
But you don’t have to use their hybrid path tracing or denoiser you can develop it completely on your own.
DXR doesn’t seem to be any more high level than Vulkan RT, if you want you can go native but it isn’t clear to me what advantages you would even get considering the already low level DX12 provides.
Well from the nvidia perspective that's exactly the point. If they figure out better techniques later they can just implement that in a driver update if everyone's using DXR. If you use your own low level thing they can't upgrade it for you.
It is nice to have for starters, but in the near future it will die quickly if somebody comes up with an improved incompatible technique, that can be implemented over existing low-level.