So I can confirm that it is locked for me as well, although I specifically remember discovering the connection "between Goblin Towns" unless my brain makes a total absolute fool out of me, hard to tell. It is very likely I discovered it during an instance though, so when the gate was accessible. I've done the quests, at the end there was the throne room with the goblin crowd cheering, with some of the access cut off, but what I remember here is that somewhere there were a door or something and I was surprised that I found myself in the old Goblin Town dungeon, one door before the throne room, at which point I was like "ahhh, so that's how they did it." But now the gate appears to be inaccessible from the Eastern side so either what I experienced in the past was some kind of a bug that seemed like a legit solution (which would have been funny) or the gate being inaccessible now is actually a bug that needs fixing, so maybe good to ask @Scenario or someone. What's up with that.

PS: Unless of course I completely imagined it or I dreamed about it, but geez, I wouldn't say it's likely!