[Whewt22]

I have an old theory which almost correlates with that. I thought that Isshin might have been sent to either investigate the hogyoku, and Kisuke may have talked him into the gigai he gave Rukia. Or he was sent for the sole purpose of hiding it due to it inability to be destroyed. Of course that gigai eats up your spiritual powers, switching it from him, who still had remenants of power, to Rukia who had just lost all of hers to Ichigo would be the quicker method of sealing it. Of course I provided plenty of foreshadowing evidence, so I still think it's a huge possibility.