I'm really not sure, maybe I missed something but why should Xemnas be capable of weilding a keyblade in the first place?
I mean he's a nobody, they don't have a heart and to gain a keyblade one must have a strong heart for all I know.
As for Roxas's keyblade it was probably Ven's heart and Xion's was a sham.
So the only way for him to have a keyblade would be if he had Terra's heart, wich I admit is very likely. But if Xemnas had Terra's heart, Terra might just supress his ability to summon a keyblade.
Guys, feel free to correct me...
I mean he's a nobody, they don't have a heart and to gain a keyblade one must have a strong heart for all I know.
As for Roxas's keyblade it was probably Ven's heart and Xion's was a sham.
So the only way for him to have a keyblade would be if he had Terra's heart, wich I admit is very likely. But if Xemnas had Terra's heart, Terra might just supress his ability to summon a keyblade.
Guys, feel free to correct me...