Blackbeard is a perfect possibility for a final villian. Oda has already stated that he always had the end in mind for the series when he started it, but its just taken a while to really get there. His character is that of a black reflection of Luffy, the same dreams, the same commitment, but a true pirate in ever sense of the world. Namely a brutal, backstabbing murderous ravager of the innocent and guilty alike.
Blackbeard is first mentioned on Drum Island as the brutal pirate crew that ravaged the island and drove out wapol.
In Alabasta he is referenced by ace.
In Jaya we get to meet him and realize that he an Luffy have a instant dislike of one another and likewise an instant sympatico. Furthermore we are introduced toa 5 man crew that fits very specific archetypes and a strong commitment to predestination, running once again counter to the self-determinism of Luffy's crew.
Also at Jaya we learn that Blackbeard gives Luffy and Zoro both the wilies AND has possibly one of the only truely menacing flag/ship combinations.
Blackbeards Crew is filled with not nice people, from Augers random blasting of birds, to Burgess's random beatings, to Doc Q's random murders.
Now we learn that while he was a subordinate of Whitebeard Blackbeard gave shanks his wound over the eye, and shanks was not being careless. FURTHERMORE, and I bold this Whitebeard says, 'looking at your face makes the wound from that bastard ache. Which implies that not only did BB wound shanks in the past, he wounded WB when he left his crew.
So now we have a pirate based on possibly the most imfamous pirate of our age, the Legendary Blackbeard (who btw was a real living demon who was shot 5 times and stabbed 23 before succumbing to a second shot at decaptation by a highlander with a broadsword, and still managed to quip before the second blow was struck) a pirate who was famous for murdering entire ships that failed to comply with his boardings. With a dream that is in direct competition with Luffy's whose ambitions are a black mirror and who may or may not Kill/break/capture Luffy's beloved older brother, who has wounded 2 of the 4 emperors.
Oh and notice how BB is engaging in his favorite activity of Town Sacking in this our latest of chapters.