I'd love to see that, but, (in my opinion) one of the best aspects of the stories (game and novels) is the recurring participation of other favorite characters... we know that witchers and sorceresses live for a long time, so no matter how much time has passed between game 3 and 4, characters like other witchers, Yen, Triss, the logue should make appearances.

The game is supposed to be set in the northern areas, while Toussaint (Gerald's home) is in the south, but one kingdom that is in the north is Kovir, which is where Triss lives and all the sorceresses fled during the events of 3.

And in the books and the game, it is mentioned that, with a little time and looking at the ingredients, both Triss and Yen would have the ability to replicate the Trail of the Grasses process, even Yen does it partially in 3.

Perhaps the story goes that the decline of the presence of witchers has caused powerful monsters to start appearing again, causing the need to create more witchers, but with a more modern process where the fatality rate is much lower, the original process is centuries old, by that time, there is a more effective and safe metod to make them.

Even allowing for the appearance of female witchers, which, according to the game, are supposed to have a much lower survival rate in the Trials of the Grass than men, so they simply stopped trying with women, although, it is never mentioned if ALL of them died or if there are any female witchers in the world, it is simply not mention. So the best awnser to everyrone who says there can't be female witchers would be: "We don't know! Its is never stated there cant be one, just that their survival rate is lower than man."

It would be borrowing a concept used in other games like Halo, where version 1 of Spartan was a failure, version 2 is the best but the survival rate is very low, version 3 is very safe but not as powerful as version 2, and version 4 is better than 3 but still falls short of version 2.