This won't exactly be helpful, and I know that no one really has a reason to believe me (seeing as I've just registered to mention this) but I have obtained this key once. Only thing is I'm not sure exactly how, though it was inspired by what was in that FAQ (Spectra Swallow, then playing with the music). I won't go as far to say it is as logical as this FAQ Man seems to think...I don't remember Kid saying anything, just grabbing the Key (it wasn't like a story event, or something like that).
Hm, come to think of it, too, the Key didn't have a specific name, it was just key. Kid grabbing it was about the extent of you having it, too, if I remember correctly (though it didn't say 'Kid stole a Key!' or something like that, I'm certain it was some kind of a generic item message with 'key' in it as Zeality said). My idea on it was that it was once (in an old version of the game) some kind of a trick to get this key to get into a more advanced debug area, but now that I think about it that doesn't make much sense.
Anyway, as far as I could tell, there is no function (so it's not really that exciting, just interesting). It must be something that was either dummied out or all access was cut from the normal game. Anyway, I just wanted to post this because I do remember getting this key. I just wish I could post more concrete evidence for you guys so there'd be 'actual' proof.
Heh, believe me or not, this is what I remember. Been a fan of the site for awhile, you folks do some interesting Chrono-related work, so, well, keep it up. 
Actually, I can back you up on that a little. While I never got any key (nor did I ever turn Kid into her orphanage outfit, Spectra Swallow eh?), I
DID turn her into her normal red outfit from the shadow by just using the music. After that, she would nod and shake her head 'yes' or 'no' as different music played, but I found no pattern to it (and I spent 3 hours playing with it after I got her in the red outfit). She would never switch from nodding to shaking
during a song, but if one was stopped and started again later she might be nodding or shaking. What the author of that FAQ seems to be describing certainly fits the overall
trend of how she behaved to the music, but, ultimately, there were flukes.
I never saw a white outfit or got a key though. I think I might've found something that helps govern it though.
One person in this thread (not bothering to find the name), made a sarcastic comment about this part of the FAQ:
Therefore, the story which effected the change was not in the story leading up
to getting into the development ending, but the one from the preceding.
The FAQ author isn't saying that the story
in the game that gets the developer's ending changes the room. He's saying that
the game that THAT New Game+ is based off of changes things in the developer's ending..
So if I go with the 'ignore Kid's poisoning and get Glenn' route, my New Game+-Developer's Ending off of that should have
differences when compared to a New Game+-Developer's Ending made off of a game where I said 'screw Glenn, I'm saving Kid' and took that route.
I've never tried that. Could be something.
