that does not show Enemy Casting Bars while you have the "hide other player spell effects" Enabled.
With the option disabled (other player effects VISIBLE), I can hide/show the target casting bar as I please. When the option is Enabled, simple using the :Show() method doesn't do anything.
It turns out that even functions like
http://runesofmagic.gamepedia.com/API:UnitCastingTime no longer function. Its as though enabling hide other player spell effects is removing/hiding the Target Casting Bar frame altogether.