Better control over the async nature of the hardware is part of what makes GPU kernels efficient, but I'm not terribly sure the same thing would be the case on the other side of the PCIe bus.

But even before you get to out-of-order/speculative execution, I think most languages lack good (i.e. non-intrinsic-based) support for wide registers or anything SIMD related. I know C++ and Rust are both working on this