Luffy most likely is incarnation of Gold Roger himself! He wanted to incarnate back to earth close to hes own son Ace. Hower the question is, had he ever met Blackbeared in another life? Roger most likely was a frequient Haki User, who wanted to play "physical" And thats what Luffy does...he plays physical
Guess the Haki too is somehow connected to how he uses hes Gomu Gomu no powers. Hower Blackbeareds Haki will also grow along the away, and he is even more crazier then Luffy
It's possible that ever Roger noticed it during hes voyages.
There obviously is no such thing as "One Piece" Hower knowing how traditional anime goes, Luffy and Blackbeared will eventually end teaming up battling even a much more impressive foe. Both are eternal dreamers, tough Luffy is pretty much still at the mental state of a little child, and Blackbeared...well him too, but hes just an
EVIL CHILD
Perhaps they will be fighting against of the other "Four Emperors" or the "Eternal Nightmare" itself!