Well, space apparently has a smell:
https://www.theatlantic.com/technology/archive/2012/07/what-space-smells-like/259903/
So I'm guessing Nomura took from this a deep meaning and substituted it for darkness. We do after all see "space" as "darkness" in Kingdom Hearts when mentioning the separated worlds. If emptiness has a smell, makes chu wonder more about the world itself.
https://www.theatlantic.com/technology/archive/2012/07/what-space-smells-like/259903/
So I'm guessing Nomura took from this a deep meaning and substituted it for darkness. We do after all see "space" as "darkness" in Kingdom Hearts when mentioning the separated worlds. If emptiness has a smell, makes chu wonder more about the world itself.