the hell.... he had acces to using it which is how he rigged it to activate he can just as easily set it to activate on any one elseItachi can't use KA. He rigged it to activate against his MS, but he can't use it since his eye is not connected to it.
kyubi's not narutos playtoi it was sealed in him hated him for most of his life, heck if madara didnt show up he'd still hate him.It's different. Kyuubi is part of Naruto now, while Shisui's eye was more like a tool to Itachi, a useful trinket.
KA isn't Itachi's power in the same way Kyuubi's cloak is not Kakashi's power. It's borrowed, not his own and can be taken from him easily.
i dont however accept that itachi will use KA and for the argument it should remain out of play.
just stating tihngs.