Random theory I realized today, probably not new though. I don't really feel like explaining too much, so i'll give you my extremely flawed logic thats probably been said 100 times.

-Kurosaki is probably a fake surname.
-Ganju looks like a young version of Isshin.
-Ichigo looks like Kaien.
-Ichigo was refered to as a pureblood, which can possibly mean that he is of noble blood.
-Details on who Ichigo's mother was and what happened to her are somewhat inaccurate, seeing as different dates were given for events by both Ichigo and Isshin.
-If one member of the Shiba clan went missing right before, during, or after its apparent fall from grace within the Gotei 13, then I dont think anyone aside from the Shiba clan would officially search for him. (Isshin)

.. and thats the end of it. Feel free to ignore it. ^^