But what about already much more popular ML-based applications: upscaling, frame generation, denoising? These are currently vendor specific. E.g. DLSS is only supported on Nvidia GPUs. Could these run on arbitrary DirectX 13 GPUs in the future by using the new API?

Granted, GPU manufacturers would likely not be keen on getting their tech on other platforms, but engine developers like Epic would clearly want to use it if they come up with their own ML upscalers, denoisers etc in the future.