Honestly this "stage discovery" doesn't seem to me too much different from when the datas of the demo were hacked and people already realized the entire cast of DoA5 (VF guests included) and the consequent missing characters from the old games. Or again when the datas of the beach stage were found with the release of the full game even if the actual level was missing.
In both the cases people ended to ask for the content that wasn't included and in both the cases in the end the requests were fulfilled (but I suppose that to complete Zack level it was since the beginning part of the plan), so I don't see why this couldn't happen even now. By the way it's true that the destroyed lab stage should be something definitely easy to implement and I don't see reasons because it wasn't never made playbale through a simple patch: it would be the most cheap way to make available another stage in the game.
I actually don't think this is anything like the content you mentioned. The beach stage and characters were all forthcoming. Fans asking for that stuff after finding it didn't make it happen, bits of data were there in the first place because it was already planned for release and people simply came across it before that content had come out, or in the case of Jacky and perhaps some of the other 5U characters, were planned for DOA5 vanilla but they simply ran out of time and included them in the next version.
"Not released yet" is completely different from scrapped content, which is what this extra level of Depth is. It's presumably something they were working on back when they were first developing this stage years ago, but canned due to time constraints, performance issues or some other reason. I won't say it's impossible, but thinking about this realistically, the odds of cut content being restored is almost non-existent. They would probably prefer to spend their time continuing to make new content, rather than tweaking old stages with content that they had already decided, for whatever reason, wasn't worth finishing. Again, I won't say it's completely impossible, but people really need to keep their expectations in check here.
As others have pointed out, receiving the alternate versions of the lab stage, which are already in the game, finished and playable would surely be more likely, and yet we still don't have those yet.
