I agree this looks fantastic, but I have to agree with Anet’s stance on 3rd party.
If they allow this script, through some kind of review or testing, then they would have to spend considerable amount of time to review and test every new update as well.
But the biggest concern would definitely be this; if they allow this script, then they’d have pressure to allow other scripts as well, then the floodgates would be open and there would be major disparities between “scripters” and “vanilla” players. They definitely want and need to keep control of such things.
I never did play WoW but I heard of the huge amount of mods available. Imagine complex scripts in GW2, ex: a mod that aims trebuchet shots for you in sPvP, DPS meters or a mod that tracks which utility an ennemy player has used in PvP.
Anyway, they could just easily implement such a thing in the options menu or make a bind available in the controls, I do support this idea.