It would be pretty cool if there are several factions for both vampires and werewolves.
Forgive me for not remembering names at the moment. I'm accepting correction.
The vampire assassin clan that is in rivalry with the dark brotherhoodan anti werewolf vampire clan cliche'
a warlock vampire clan. basically like necromancers and use a lot of dark magic. Maybe the leader is in a castle like Dracula?
an anti vampire werewolf gathering cliche'
free roam innocent people that became infected and unintentionally become overwhelmed and out of control werewolves once in a blue moon. (should all werewolves change only on full moons?)
werewolves that hunt in packs, generally coordinate attacks on villages for food.
Vampire slayers
Expert Hunters that are accustomed to fighting werewolves and other beasts
Other werecreatures
The return of the wereboar?
the rumored weresharks?
It wasn't a vampire clan technically that were against the Brotherhood, it was more of a splinter faction composed of vampires led by Greywyn Blenwyth who signed on just so he could overthrow the Black Hand and turn everyone into vampires. He formed the Crimson Scars, which they got their names from slicing people's neck with jagged blades! They were pretty powerful according to Greywyn that not even the Dark brotherhood knew about them. Until Silarian decided to betray the Crimson Scars because he was pretty whiney about being a vampire, so he tattle-taled on the Crimson Scars and the Dark brotherhood killed the Scars when they were all sleeping. So far we know the survivors were Rowly Eardwulf and Greywyn. Rowly survived and stays at the Wawnet Inn, but Greywyn was killed just before Sithis was going to accept the Scars. Pretty messed up if you ask me, Greywyn had to renouce is vampirism in order for his blood-svcking faction to get accepted, as soon as he was going to pray to Sithis, they stabbed him in the back. Ha.
But I would like to see the Scars come back. Maybe rising after the chaos in the Dark Brotherhood started in the Oblivion events. I mean what's 200 years for a vampire?