I am curious with something that is so easy; why would you want it in core?
A lot of the Math Functions could be considered "so easy".
abs() could be written out as:
function abs($n) {
if ($n >= 0) return $n;
else return $n*-1;
}
pi() could be replaced by simply setting a global variable equal to 3.14159265358979
floor() could be written out as:
function floor($n) {
$stop = strpos($n, '.');
if ($stop !== false) return substr($n,0,$stop);
else return $n
}
ceil() could be written out as:
function ceila($n) {
$stop = strpos($n, '.');
if ($stop !== false) return 1+substr($n,0,$stop);
else return $n;
}
The above examples are just a few that stick out to me I'm sure that looking through the list of available math functions would provide a few more examples. Keeping these examples in mind, I don't follow the logic of range mapping being too easy to implement manually whenever it is needed to not warrant being included in core.