What Could Have Been: The original third series before it was cancelled. According to series director, Joss Agnew, it would have contained Vlad 'alive' and dealing with his destiny, Ingrid leading a teenage vampire army, and Stokely in flames.
Ingrid leading a teenage vampire army is touched upon in the revived series 3 when she bites a group of schoolgirls and uses them as a posse to try to kill Vlad ("Vampiress Liberation!").
Word Of God: The director of the show, Joss Agnew, was very involved with the fandom during the show's second series. He actively commented on the IMDB boards, took part in discussions, gave cryptic spoilers, and would often send screencaps to those who requested when he had them up for offer. Fandom opinion is that he's awesome.
A few of the actors will give some clues to what will happen on Twitter a few times, Clare Thomas who plays Ingrid Twitting a lot of clues in the lead up to series 4.