It'd be so cool if they had a Witcher themed mmo. Geralt wouldn't be involved obviously. This could take place before his time. There's so much lore they could play around with. Different realms/worlds. Several playable races and classes. With the possibility of factions for PvP. As well as countless options for PvE. You have different witcher schools with unique traits:

School of the Bear (Loners. Focused solely on the job. They favor heavy armor so more of a tanky heavy hitter character. Be able to withstand damage as well as deal it. Other than Cat, they're the only ones who are known to use crossbows).

School of the Griffin; Also Known as School of the Eagle (Similar to the School of the Wolf, but more focused on magic. With a library with extensive knowledge on magic. They too follow the strict code of neutrality, kept their original 'knightly' values of the order. Their focus was magic, preparedness, and flexibility. Due to their strong bonds with each other and emphasis on team effort, they'd be perfect for a more support oriented character).

School of the Cat (They were the first school to produce women witchers as well as accepting different races. Started out with noble goals. That changed later on due to their warped mutations and time spent with the Aen Seidhe. They favor agility. But are more a Jack-of-all-Trades. Flexible with their fighting syle as well as their morals. Would be perfect for rogue/assassin type mercenaries due to their loose morals. They take part in nearly anything as long as there's coin invlovled. Due to their ties with elves they tend to be more disdainful toward humans. Accepting contracts more readily from elves).

School of the Viper (again would be perfect for a rogue/assassin character or mercenary, they have loose morals similar to Cat. Anything for coin. They favor poison coated daggers. So they're adept at alchemy as well. Especially when it comes to concocting different poisons).

School of the Manticore (They produced pure warriors. So they'd be fit for a more tanky or heavy hitting character)

School of the Wolf (The most famous due to Geralt. One of the most organized schools. They forged strong bonds with each other. A pack-like mentality. So would be good for a support tank type character or melee dps oriented. They stayed true to their origins. Never get involved in the affairs of men. Kill monsters for coin).

Then you have the Brotherhood of Sorcerers who's largely political. You'd have different kingdoms to play around with. Each with their own customs and laws. You could have different types of mages that specialize in different forms of magic. Elemental or dark/forbidden magics (necromancy or blood magic). Maybe the story could differ depending on what kingdom you're assigned to (of your choosing).

Druids; Scholars of the Forest. Are human or humanoid creatures specializing in nature magic. Typically peaceful. More focused on healing and nurturing. Can be either male or female. There are different circles of druids. Healing and buffing type class.

Dryads; Nymphs of the Woods. Purely female. Can be different races. Made up mainly of hybrids. Isolationists. Pefers to remain in Brokilon. Specialize in nature magic to heal. Also specialze in archery. Transformed dryads or Naturalized dryads are a sub-race of dryads with an even deeper connection with nature. So possibly a healing/buffing support class.

Priests/Priestesses; They consider their talents 'God Given' or 'Gifts Bestowed from the Divine.' Used to heal people, their focus is for the 'good of the people.' So priest type healing class or paladin/templar type. 

You have several possible races to play as; Humans, Elves, Dwarves, Halflings, Gnomes, and Vampires (True Higher Vampires as well as a few Higher Vampire Subspecies. Such as a Bruxa). Possibly others. Each with a unique set of skills, strengths, and weaknesses (racial abilities) and available factions (Witcher, Brotherhood of Sorcerers, Dryad/Druid, Priest/Priestess, an Independant Mercenary). You'd be treated differently depending on race and faction. Have backstories similar to Dragon Age: Origins. Not to mention all the different types of creatures/people you can interact with. Several creatures/monsters to fight against; Vampires (all the different subspecies), Sirens, Kikimore, Werebeasts, Striga, Ghouls, Succubi/Incubi, Lamia, Wraithes, Wyvern, and many others. Along with the different wildlife and hostile humanoids.  

Possible professions to make a living. Cooking, alchemy, bounty hunting, blacksmithing, tailoring, woodworking/carpentry, hunting, and bard. Along with being able to murder and steal (at your own risk). So a justice system would be in place. It'd be another way for bounty hunters to make money (killing outlaw players) rather than just killing monsters or npcs.

The possibilities are endless.

damn i want to be evil elves or evil witches or vampires

Haha, right? It would have the potential of being far more mature and dark than Elder Scrolls Online with deeper roleplay. The option to be good, evil, or neutral is always good.

no, i mean the evil elves able to travel between worlds and dimension and spread eternal winter

and for witches it is more 

The Aen Elle (dark elves)? Like the Wild Hunt? Because that'd be really neat! Same with the witches.