While this could be for either the Xbox 360 version of The Witcher 2, or making DLC for the PC version, there's evidence that the company is beginning work on The Witcher 3.
According to Gamepur, Jan Bartkowicz stated, "Consider this example, for comparison, films like Pirates of the Caribbean, where the first (has a) self-contained story, the later is unchangeable, but then you think, it should be a trilogy. So people have a problem then. The end of The Witcher 2 is the beginning of much larger events, while The Witcher (had) rather a cliffhanger ending."
Stay tuned.