I did'nt go into that theory that Kaien would be Ichigo's reincarnation, and I don't want to...
If it's true, honestly Bleach would be ruined for me
The fact they look alike (appearance and personality) is more than enough as a correlation. In the other side, a relation involving Ichigo's Hollow and Kaien's would lead to some twisted plot...
I really don't see how their Hollows could be related; the time and various dates Aizen mentions in the last eps must be matching Kaien's death/Ichigo's birth and so on, to be enough as a solid theory