Not sure why SIMT would help, it requires more compiler transforms than if the code is written for packets/vectors or whatever we want to call them. As you note

Not sure why SIMT would help, it requires more compiler transforms than if the code is written for packets/vectors or whatever we want to call them. As you note, cross-lane is a key part of a good SIMD abstraction. Vulkan calls it "subgroups", but from where I sit it's still SIMD.