For me, why Kakashi killed Rin.
Obito's motives have to be more than just her death. He's been alive this whole time, so maybe his clan being slaughtered is another reason he's doing this. If it's just for one girl then that's... really stupid, and I seriously doubt it even though many people say that's why he's doing this.
I'm also curious about the whole panel in chapter 616 with Shikaku. Was it really necessary to add it? Threads are being made about it, so it really caught people's attention.