about Lion's Arch Keep

I don't remember being able to access the zone before the WiK stuff, has it always been there? Was it designed just for the event or was it some old zone that was cut out from the game, and recycled for the occasion?

We didn't have access to the keep prior to WiK. Can't really say whether Anet made it ages ago and reused it but I doubt it. It seems to fit the purpose too well, but then again it may have been tweaked. Then again, if they had made it for Prophecies they probably would have used it. It's a pretty important location.

I'd say it was there as background - the hills and terraces where there. Then, Anet used this baseline and added details that are now visible. So, it half existed.

Well, my idea...

I think it was always there they just gave us acess, they might have been like "so well design this because at some point the keep will play a role" then they populated it with people and story come the wik stuff

^^
This.

Just like in UW, in the Ice Wastes where Dhuum now resides there were just doors there. You could walk right up to them zoom your camera all the way in & "peek" through the doors, there was nothing behind those doors except the empty landscape of the Ice Wastes. After the addition of Dhuum to UW behind those doors is now his chamber.

They added the lab area near Shaemoor and expanded Dakutu Village. So I believe they added in the keep also.