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Maybe its something less precise:
Three Doors (i.e. the one in DI and both leading to the KH we know from 1 and 2)
Edit: just a crazy suggestion: Re: 358/2 Days - Sora's Heart (that would explain rather strange events, and Riku coming up as a protagonist)
huh....i'm so glad kh3d won't actually be in 3d, and that it's just a working title, abbreviation thing. despite popular opinion, i hate 3d. but i digress.