I do not think Mayuri would say you "failed" to kill someone who is stronger or just as strong as the commander. More likely some feelings were involved - the first disciple, the most promising captain, etc (Not I am your father, please). The commander failed to kill someone in the past, regretted it and so was ready to go all ruthless on Rukia, on the captains that opposed Rukia's ruling and then burn Soul Society captains along with Aizen.
And since this is the final plot Ichigo's origins have to have something to do with it - the common roots of Quincy, Arrancar, Shinigami powers, etc.
Wanna see the grown-up version of Neil! And I wonder about Ishida and his father now that the Quincy involvement is obvious. Have to wait until the end of the Golden Week, though.
I think he's his father.......
"I got rid of my teeth at a young age because... I'm straight. Teeth are for gay people. That's why fairies come and get them. "
Aqua Team Hunger Force
I'm thinking that Ichigo's going to learn some Quincy skills or sort since the current enemy is Quincy.