If you really want to flip the sort order of upper/lower case, you can invert the case of the string, then sort it, then invert the case of the sorted-string.
Code:
alias invert_case return $regsubex( $1- ,/([a-zA-Z])/g, $chr($xor($asc(\t),32)) )
//echo -a $invert_case($sorttokcs($invert_case(z A b a Z y),32,A))
