I think its extremely evident some level of Rocks is within Blackbeard. Either just straight up will of D as a concept (like how Luffy literally says the same things as Roger without being directly related to him), so somehow Rocks really is alive through his son somehow.
The incident with Imu says it never happens again, yet Oda has him declare he'll be back. He then talks again to Harald in the same manner, but suggests that if its him to do it, someone else will.
I really hope this continues through God Valley. Within 6 years Loki needs to get rejected again and Rocks ends up "dying". I just hope that this is the final flashback tied to God Valley and we dont need to wait until Blackbeard or Shanks or something.