Sometimes I wonder about an alternative history scenario where CPU ISA's would have chosen a SIMT style model instead of SIMD. "Just" have something like fork/join instructions to start/stop vector mode, otherwise use the standard scalar instructions in both scalar and vector mode. Would have avoided a lot of combinatorial explosion in instructions. (of course you'd have to do something for cross-lane operations, and later tensor instructions etc.)
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.
