im nto sure, duran COULD be a xel naga, after all maybe the xel naga sent him to do something with both of their failed creations so that they could finally b powerful and kill off the zerg and protoss since both of them betrayed the naga.
duran definitely has some connection to the Naga, but it seems more likely that he is some kind of saboteur working against them,the zerg, the terran, and the protoss. the hybrids(if a species in sc2) will more than likely be the main enemies, and i have a funny feeling that kerrigan will end up at least cooperating for a time with all 2(maybe 3?) other races against the hybrids so it will be an epic battle against the big evil, kinda like wc3 in the last level human/night elf/orcs form up against the undead scourge, whereas before in all games there were no alliances between them. duran probably stole some xel naga secrets or something like that and is using them to create the hybrids. he will more than likely be the 'bad guy' of sc2, like kerrigan is in bw and the overmind is in sc.
just my 2 cents.
oh yea, scfan13, you say you saw an official site that definitely says naga and hybrids sc2 races, would you care to share it with the rest of us since to our knowledge blizzard hasnt announced sc2 yet?