100%, I'm not anybody in particular but I've been saying this for years, as soon as I saw Spectre/Meltdown announced it's like "lol yeah I bet GPUs have zero hardening against that sort of thing". I hadn't thought of the connection between Meltdown and that person's comment but it's entirely possible the Intel team was deep in Meltdown at that moment when they got presented that lol.
Also Intel in particular seems to have uniquely tight ties between the iGPU and the CPU, since they come from a world where dGPUs didn't exist and the iGPU was only ever a ringbus away from memory or the CPU... it's apparently been a huge problem with the Xe/Arc drivers (there have been a couple patches where they produced 100x speedups by fixing operations that allocate memory in the wrong place, etc) since the GPU is suddenly no longer super close. It would not surprise me at all if AMD would be more secure because they're not working with an iGPU that's super tightly tied to the CPU like that.
https://www.pcworld.com/article/819397/intels-graphics-drive...
But yeah anyway I totally agree, multi-tenant or multi-privilege-level GPU is likely a shitshow, so in a way it's actually a blessing that heavy GPGPU compute never really took off. Because I bet you can totally do things like leak the desktop or your browser windows to malicious webGL or another tenant on a shared vGPU. We live in a world where clients are mostly running one GPGPU application at a time, plus the desktop.
(Although of course, it's always a little useless to speculate about the world going completely differently... if multi-tenant/multi-app GPGPU compute had taken off, more attention probably would have been paid to multi-user security/hardening.)
I am willing to bet that NVidia and AMD's GPU unit have floodgates of vulnerabilities along the lines of Spectre, which they simply never had to deal with before (not to mentions likely hundreds of more basic ones).