When I started my light elf back in c1 I wondered the same thing. Level 10 and not having explorered the world of Aden to much I embraked on a quest. I literally travled the map by foot. My adventually desination was forbidden gateway. I surprising didnt die til I got their either omg cemetary is scary at lvl 10 even back then.
I clicked to town and headed out to FG again now being very careful and made it up to the actually forbidden gateway. There was nothing just a wall!
I wondered then if you had to defeat a boss or something but alas nothing and I always thought back then they should incoporate something for it, but as years went by and FG stopped even really being a place people hunted at regularly(FOTD kind became the new hotspot after it came out) I forgot about this idea.
I think many players who are into exploring had a crush on Forbidden Gateway, sadly up to this day it holds its dark secrets locked :( Hopefully one day those gates will open with a grand opening.
More likely something from the sky falls down and wipes that FG from the ground. Making interesting and exciting new locations without destroying old ones is not what developers want to do now.
Maybe someone can lend them money so they just make a copy of l2 and turn it into new project leaving us to play our lovely game as it was designed.