MANGA SPOILERS THROUGHOUT THESE SPECULATIONS.
There have theories floating around longer than I've been in the fandom and that's a long while. Many of us threw out the Kaien=Ichigo idea when AAroneirro showed up with Kaien's soul-body (there are other possibilities but if Kaien's soul-body was inside Aaro then according to some law of the Bleachverse about reishi occupying the same soul-bodies at the same time, it seems like Kaien couldn't be Ichigo--right?)
Recently, Kubo-sensei revealed in interview that he had a large role in the closing lines of Fade to Black which contained Ichigo's postulating about a previous connection between himself and Rukia. This is how melodymix translated the crucial phrase from the novel that was just released to accompany the movie's release:
"...Hey, if death really isn't the end, even for us maybe that was not our first meeting... maybe we were connected way before that"
What I find interesting is that while some people call this Ichigo's answer to Orihime's Five Lifetimes speech, it's really a very Kubo-esque parallel. Orihime presumes/imagines that she would love Ichigo for her next five lifetimes--note that this is something that hasn't occurred yet; it only exists in her imagination; it is only hopefulness and girlish wishing.
Meanwhile, Ichigo presumes that he and Rukia have already shared lifetimes. The intimacy and connection has already occurred.
If Orihime's words were shown to be unequivocably romantic, then what about Ichigo's?
True, one occurs in the manga and the other in the movie but after Shishou's level of involvement in the movie, his talking about how he fussed over those very lines at the end of the story, how can anyone doubt his intentions?
I really wonder if reincarnation is going to play a part in the Bleach manga. So many of us dismissed the Kaien=Ichigo theory long ago and claim to dislike the reincarnated idea because it somewhat belittles the connection that Ichigo and Rukia built up here in this one lifetime, but given the hints, is it possible that Kubo-sensei may still go that way?