There’s no “stonewall” in any way since this is simply about the capabilities of iommu in general, how it works and how bios vendors configure it. Mosaic needs p2p communication, virtualization needs device isolation.
Robert Crovella of Nvidia explained this a long time ago, check this thread:
https://forums.developer.nvidia.com/t/multi-gpu-peer-to-peer-access-failing-on-tesla-k80/39748/10