Nomura had already said in the past that KH would end, and he already has the ending in mind. (hopefully it ends at 3)
Memory Master:
I think that's pretty much it.
As for WHY Ven's heart would be in Sora, it defiantly have something to do with the 'erase me' comment Ven gives. I'm still sticking to the idea that he wanted to die, but instead, someone wanted him to live so they erased his memories and kept his heart someplace safe, away from the war and so that he may have the childhood he probably didn't have; In a young boy, on a Island, in the middle of no where.
Yea, like Sora did.
Why can Sora have two blades? Because he holds the hearts of two keyblade weilders. Ven, and his own.
Riku also had two blades for a short while which lead me to believe he has two hearts too. But how?
Master Xehanort's heart.
Going with the MX + Terra = Xehanort theory, the heart that becomes KH1 ansem, posses Riku remmeber? And that heart never left. It still resides within him, he just has more control over it and since Master Xehanort was a weilder...
Riku's heart, + MX's heart = two blades.
Q: But why didn't Xemnas have a keyblade? Because he is a honest nobody with no heart. You need a heart to hold a blade.
But it also brings me to the question: What happened to Terra's heart? Did it become one heart with MX or it resides somewhere else like Riku's went to KH?