or is it someone in the past. I mean there are so many, are they just part of one bigger being? Is that why they say that sora is incomplete? There are so many things that we have yet to be answered, remember there are 2, the one that walks to salvation and the one that walks to the road to destruction. (We think that sora is the one to salvation but is he? Is riku the one that walks destruction?) we don't know.
Like you say. It is unknown. Sora may have good intentions, but may in the end destroy everything. Riku fell to the Darkness, but may fix what Sora may do if Sora is the one that leads to destruction. Also, you can't forget BHK. Where is he in all of this?