Mx in place of Mr/Mrs/Miss/Ms doesn't completely solve the problem of gender identification. My father-in-law was Polish and while his and his son's family name ends in "...ski", my wife's and her sister's family name ends in "...ska". An alternative of "...skx" is not on offer.

Nor for members of Icelandic families whose names end in 'son' or 'dottir', depending on gender.