As someone who implemented an open source quicksort (http://www.mqseries.net/phpBB2/viewtopic.php?p=273722) which is used by many in production:

Now this is very interesting, but could also be prevented with a random number generator (which influences the selection of the pivot element). If this would have been exploited, people would have looked into mitigating this.

Edit: You can detect recursion-tree-degeneration (just check the depth) and react to it (pivot selection)