It will never happen, because there's no (relevant) IP attached, but Journey to the Center of the Earth is easily the attraction I'd most like to see take the expansion pad in Adventureland. A new Indiana Jones ride concept would be a close second (if not put in Hollywood Studios).
Not to derail, but does the Defunctland guy care about or like anything?
I applaud how well-put-together a lot of his content is, but that's the general vibe I always get from it.