On the flip side, until somewhat recently, NVIDIA GPUs didn't have the kind of hardware protections you'd want to build a modern multitenant OS (e.g., hardware page table and TLB support).
In the actual tweet (https://x.com/ID_AA_Carmack/status/1865127952712905197) he mostly seems to be talking about RLO style diagnostics with busybox on the device much like Dell servers with fancy BMCs:
> I still think today’s GPUs should be able to operate without host CPUs if they have a private link. Chains of accelerators are a legitimate use, but it would just be fun if GPUs made their own video signal with diagnostic information when you apply power outside of a host system. You could go farther and put a tiny linux system running busybox on your command processor, and backchannel keyboard input through the display port if you don’t have a USB port.