This is something that I've been wondering since the end of 3D: will Riku ever wield the Kingdom Key again? The Kingdom Key was originally Riku's Keyblade, but because of his choice of darkness over light in KH1, Sora received that Keyblade; leaving Riku to find his own path and receive the Keyblade modeled to represent his journey back to light: The Way to Dawn. But now that Riku has proven himself as a Keyblade master and is no longer tied to the darkness, shouldn't he be able to wield the Keyblade he was originally meant to wield? Also Riku was using able to use the Kingdom Key to wake up Sora at the end of 3D. I get why, that Keyblade was aiding Riku in helping Sora, but it's when Riku used it after talking to DiZ that makes me think this. Sora was already awake and if Riku needed to use the Kingdom Key to help Sora, why would he still be able to use it when Sora was awake? It's probably nothing important but i find it really strange and interesting.

So, if Riku is able to use the Kingdom Key in KH3, what will Sora use? Well, here's where the Key to Return Hearts comes in. We no nothing about this Key, and Nomura has said it might not even be a Keyblade, but I'm assuming it is. I think that the Key to Return Hearts is the Keyblade that Sora is meant to wield. In KH2 Yen Sid said that Sora was the "Key that connects everything", he is the one that connects all the events and people in the KH series. He's going to return everyone that has lost their way, so I think it fitting that he'd wield a Keyblade with such a name.

I do like Sora with the Kingdom Key and Riku with the Way to Dawn. But with the complex history of the Kingdom Key and the introduction of the Key to Return Hearts, I can't help but wonder if they're going to be wielding different Keyblades in KH3.

I think the Kingdom Key at this point has found a comfortable home with Sora, to the point where there's no need for it to go back to Riku.

After Sora said his friends are his power back in Kingdom Hearts 1, the kingdom key officially abandoned Riku and chooses Sora as his official master. Sora has proven himself that his heart was stronger than Riku so I said no Riku won't wield the kingdom key keyblade. Riku has come a long way to gain his own keyblade and Dream Drop Distance proves that Riku was worthy to wield the keyblade but wield his own keyblade power.

Well, Riku hasn't lost his ties to the darkness.  Rather, he has mastered the darkness that he could not control, which makes him that much more of a powerful Keyblade Wielder.  I'm pretty sure that Sora will stay with the Kingdom Key, as it has become symbolic for Sora to wield it.  And as for the Key to Return Hearts, I really don't know how that will work out, but I'm sure it'll be something surprising!