If Aizen was plotting all this time to bring out hollow-kaien, then that means he would've planned on some reincarnation of kaien to come to soul society in the first place (which i guess ichigo could be, since they mentioned the resemblance). I dunno, sounds infinitely impossible for anyone to plan for the sequence of events that lead a young boy bearing the characteristics of an ex-leutenant that also awoken his death god powers while simultaneously turning into a hollow who entered into the mix to begin with from an interaction with a death god whom lent him her powers.

Even the people who helped train ichigo didn't realize the hollow side until yoruichi saw that mask after the kenpachi fight.