I believe my feelings at the time of playing kingdom hearts 2 were that if I played kingdom hearts 1 again with the knowledge of nobodies then you'd expect things to happen that didn't. The whole concept was tacked on in KH2, and I don't really mind, but to go say that it's a terribly fruitful subplot is a bit much. Other random things didn't make any sense. The heartless existed before Sora left his island, was Sora the first to kill one, ever? Sora's not even the only one with a keyblade. Then Roxas being used to restore Sora was weird as well. It was just a convoluted. It seemed to be an attempt to throw an existential plot curve our way but you need to make things like that planned out from the beginning when you're building a plot up so you can tear it down effectively instead of making people go, "Huh? That doesn't work."
I agree with you in that some of the plot was a little underdeveloped. I don't think they gave Nomura enough time to realize his original goal of KHII. He did create the movie hinting at it for the PAL version, since it had sold so well in Japan. But before that he had to create a game that would/could stand alone. In fact, I remember reading that originally you fought Malificent and that was the end. Thank god that didn't happen.
The whole past and the mechanics of the KH universe is a bit hidden. Hints are there, but it's mostly vieled. For example, when you visit King Tident he instantly recognizes a Keyblade and scolds Sora for bringing "one of those" here.
The Heartless and Nobodies existed way before KHI even started. However, they had just recently invaded that corner of the universe. Ansem, with Xenohart, had been experimenting on them at the behest of Xenohart. Hm. I believe that Xenohart created a way for these 'nobodies' to become sentient after their detatchment from their heart. This is why we have characters like Axyl and Siax and even Roxas, but Roxas & Namine were created through a special circumstance.
I try to understand the idea of multiple keyblade bearers is that each person, with a pure heart, can call a keyblade from the void (or wheverever they come from). Sora called one when he needed to defend his friends from a heartless invasion led on by Xenohart's heartless. Riku had to call on one to save himself from the darkness, even becoming a heartless himself. Riku is a very complex character, one of my favorites. Mikey has been trained to be a keyblade bearer, in fact, he may have the purest heart in all the universe. Who knows.
I know there are a lot of unanswered questions, but most of them come from the past. What happened during the keyblade wars? What, or more importantly, who was Xenohart before he washed up on Hollow Bastion? Is Roxas an extension of Sora's personality, or a completely different person?
I'm afraid I only have more speculation for those questions. Hopefully they'll be answered in KHIII or whatever they decide to name it. Personally, I believe the secret ending is the 'past,' during the keyblade wars. The man with brown hair is Xenohart (and mayhap, be Sora's father). The blond-haired and blue-haired person are his friends.
Sorry, I've turned this into an analysis. XD
P.S.
If you pay attention to the trailer, when the Blond-Haired-Knight is frozen his/her eyes move ever so slightly. That person isn't dead, methinks.
and where's the badguy from Tarzan's Nobody. He had a Heartless form that retained his shame seemingly showing his heart/body strong enough to be similar to Ansem Heartless or Organization XIII...
