Hey, my old thread has come back.
Aren't most of the protagonists already counted as such? I mean except for Shanoa there isn't really any question for the others since they're either partners that don't wield the Vampire Killer or they are members of families indirectly related to the Belmont line.
Not quite. Alucard, Eric, Nathan, Soma, Charlotte, Hector, Shanoa.... For the sake of naming a few. Unless that's what you mean by "partners that don't wield the VK".
My theory is that all protagonists are descendants of the Belmonts but they don't know it. 
The next major CV plot twist:
... Nah. That would make it all seem so utterly uninteresting. It's part of the fun to get to know the character you're playing as, and to understand why he was chosen in the first place.
Maybe CV's storyline isn't as pampered as in Konami's other flagship series, but we'll have to make do with what we have. If our Castlevania lore won't be handed to us in its 'official' form, we'll just have to make it up. Another reason why I consider it to be a crime that the CV fanfic site isn't more populated...
And speaking of continuities, why don't we just implement our own "Dungeon Timeline", just for the hell of it?