Indeed, and that would make the code machine-dependent too. On top of that, BLASFEO is already used for the most computationally intensive operations (e.g. matrix-matrix operations and factorizations, involving O(n^3) flops on O(n^2) data) providing high performance and low overhead, and the other operations on vector and matrices are anyway usually memory bounded and would see little to no benefit from directly using the assembly language.