I agree. I'm not really for Harrison getting his own Dark Passenger either. For all the similarities w/ the birth of Dexter's own Dark Passenger, Harrison's was very different. Dex witness four violent & bloody murders at the age of three then was left among the corpses for two days. Harrison is less than one, likely never saw much violence done to Rita, and was left alone for a few hours. Unless the series turns to the supernatural like the books do (go check out Wikipedia) then I think giving Harrison his own Dark Passenger would be a big logic fail for the series.
I didn't read the books, but did read the Wiki entry, so of course I'm well versed. Anyway, the parallels were great between Dex and Harrison in that final scene of this season, but I don't think there were enough to birth Harrison's own Dark Passenger unless it does go supernatural, which would be an interesting 180 for the series.
Personally I'm hoping for no time jumps between the end of this season and the beginning of next season. I'd like to see Dexter learning to become a true father, and not just a "pretend" dad like he was when Rita was around, and begin to try and rid himself of his "dark passenger."