You're still running untrusted code on the same devices. IOMMUs aren't enough, not since side-channel attacks entered the field, not to mention the consistent a

You're still running untrusted code on the same devices. IOMMUs aren't enough, not since side-channel attacks entered the field, not to mention the consistent availability of IOMMU and Secure Enclave bypasses, or exploits for the GPU to access data from other contexts.