I was mostly referring to the parent comment's suggestion that low level numerical libraries wouldn't benefit from a pure Julia implementation, specifically to the statement that it was still better to write optimized C/FORTRAN and call from Julia. Indeed, MaBLAS, which you linked, is built on top of LoopVectorization.jl.

I don't know how well ArnoldiMethod.jl compares with ARPACK, but if there is a gap my suggestion is simply that these recent developments might help bridge it :)