Light Aura said:
Since Sora has a strong heart he can use a keyblade. Although when he drives he can use two keyblades except in wisdom form. When he goes into brave form wouldn't it be possible that he borrows Goofy's heart to form another keyblade? If that is true then Goofy's heart is strong enough to use a keyblade. I think the reason he can't have a keyblade is because Sora already has the keyblade of light. This could also be the same for your other party members. Other people besides Sora could have a heart strong enough to weild a keyblade, it's just that Sora's heart is stronger than other people's hearts.
My friend and fellow conspiritor, Mitsukai, has already posted a theory on this. It is as follows: The keyblade is actually an extension of the heart: Anyone can weild one, if their heart is strong enough. Sora's became strong enough because of his love of his friends, and Riku's became strong enough because of both his lust for power, and because Ansem was contained in his body with him, and so their two hearts overwhelmed Sora's heart.
The Keychains are not so much attachments, but symbolic of the Keyblader's memories, for example, Jungle King was symbolic of Sora's memories of his time in deep jungle, because he focussed him memories on the object, it gained the power to change the form of the keyblade, as memories change the form of a heart.
If you extrapolate on this theory, it is possible for anyone to, if their heart is strong enough, weild a keyblade, and is possible for Sora, and indeed anyone, to change the shape of the Keyblade with their Memories alone. This would also explain why Sora was unable to use all his keychains in CoM, and instead made his kindgom key stronge with the memory cards of other keyblades, and would also explain why you have few keychains at the start of KH, because in both instances he has temporarily lost his memory.