I don't know. Going by the secret ending, Ienzo seemed to be suspicious of Xehanort and Braig. So maybe Ienzo didn't really betray Ansem, maybe Ienzo only pretended to betray Ansem in order to get close to Xemnas and Xigbar and find out what their planning. Going by the scene with Xigbar and Zexion in KH2FM it gave me that same feeling. I think there is more to Ienzo/Zexion than we know. So Ienzo/Zexion may still feel close to Ansem as he only pretended to turn against him, But I would say Ansem believing Iezon turned against him truly he began to hate him.
Yeah. Although Nomura originally said Zexion's weapon was important, he kind only said that as a marketing strategy. However, it is possible that because Zexion and Izeno are such mysterious characters, perhaps his book might have further research Xehanort and the other apprentices did on darkness of the Heart. If this becomes true, than would it be that farfetched that Izeno might give it to Sora in order to help him out given what we now know about his connection with AtW?