First of all I need to say it is a very good and solid game. With a great atmosphere but ... for me as it is now it is not finished in some parts (and the Triss part is one of them).
The good thing is the main Story is finished and the endings are very good. Not like other games. So I was not frustrated after the game but disappointed.
I'm with you that Yen needs to be introduce, but why in this harsh way. Why not with a flashback scene as they meet the first time hunting the dragon ... or as she meet Ciri (a very linear quest with no much choices).
So you get both Ciri and Yen better introduced. And to be honest why not the choice at the start being more interested on Yen, or more on Triss.
Up to this choice Triss react in another way when you meet her. And chose later the game as it is now, who it will be. And some more lines of conversations for Triss
Of course that would mean more work but to be honest to choose between a game 100% finished and 90 or 95% like it feels now I prefer to wait 6 month more and get the 100 % or 105 % and not 90 %.
And I am sorry to say this abou this real good game but ... somehow it feels like there was space left so that there is enough space for modders to add content or for DLC content. But this was hopefully not the intention even if it feels for me like this.
I totally agree because it could not be the job of modders to made the main persons of the game better and more interesting (Yen, Ciri and for me more important
Triss).
Mods for more monster slayer quest or to rescue persons maybe based on some novells, swords, amors and so on yes please as much as modders can do, but the main persons ... very difficult and to be honest I m lazy with reading and to get the very good voices on the quests for the main persons or other content from modders is for modder impossible!
So lets see what will come ... I hope the best but expecte not really much ... we'll see ...
PS: I hope that for the next 2 or 3 years every 3 or 6 month comes and extension like the one which is announced for october. So let the game never stop
PPS: I palyed the games and also read the books and I never liked Yen and I will never like her ... thats why I was happy to choose Triss in the Games. But I got really disappointed what and how it was in Witcher 3 and there is no connection to the great awesome undescribable work in Witcher 2.