This was indeed an amazing shuffle.....Sayaka is just so much beyond being an idol now, its unbelievable.
As for Sae`s reaction...at first glance, this is the best way for everybody. Management gets a desperately needed front girl and leader for K that will lose much of its starpower and leadership this year, while Sae can keep closer contact to japanese fans. At second sight though, at this moment she might have realized her dream of becoming the well-respected captain of an 48 sister group is _really_ over. I think she secretly wanted to become the Sasshi of SNH
. Now she is at the point again where she was 6 months ago. Meaning, she is going to be a well-respected former-Senbatsu-now-theater-senpai. And that was not on her to-do-list i guess. People tend to forget that Saechan is a very ambitious woman, and when she said some months ago, that she doesnt want to come back before she achieved something, she was pretty serious about it.
Sorry for tl/dr.
Good news is, the theater wall already was updated with her picture, and its clearly the best portrait shot ever: