chapter 252 came out! LQ, but scanlated enough to understand it. xD
"What I know...has got nothing to do with you." -Bleach, ch 239
Genryusai clearly stated there were a few things required for Aizen to enter the realm the King is in.
Something along the lines of, a large area rich with souls, a million mod souls, and something else. Then he could enter the realm and possibly kill the king. Then he estimated that it would take place during winter.
I the it was the "KEY OF THE KING" I suppose that it helps open the dimension to the king's place or something.