All this talk about darkness is making me think of BB. XD Stop it.
But actually, I think the weakness will just make us all go "WTF?" or "Oh, I predicted that. Someone give me a cookie"
But yeah, my first guess would be too much light. I mean, shadows don't exactly appear in the morning. And, it's nearly dawn in One Piece, so…I'm not sure.
Can't wait for the spoilers. Whether they're today or tomorrow, I'm dieing to know Moria's weakness.
EDIT
:::
Wait, I just thought of something. Not related to Moria's weakness sort of, but I'll throw it out anyway.
I think next chapter, Oda is going to go back to the Odz and Moria vs Strawhats fight. Then later, Luffy appears with possibly his new form thing (afro luffy, mizu luffy, etc, you know what I mean) and be like "MORIA!! This time, I won't lose! I know your secret!" and it will be revealed? XD I dunno.