The thing is, the expansions were announced a month or two before the game was released and our complaints could have been noticed, and I would guess already have at least a general idea of how things will be and the over-arching story line of them. and there's a good chance, that because of the fact that only now they hear about the Triss-relationship complaints it's too late for these expansions to be changed or altered other than some token appearance.
In my perfect world, if a Djinn will ask me for a wish regarding the witcher DLCs or expansions, I would say, a short-but-sweet DLC in Kovir, where it start with Triss & Geralt together, Ciri (Be it an empress, a witcher, or Avlach come instead) comes to visit and asks for help from both of them and they have a small quest, you could even end it with a sex scene for some more fan-service.
Point is - a DLC for the romance option be it Yen or Triss is not that far fetched idea, all we need to prove is that people want it
I'm not saying it is far fetched I'm saying I doubt it because romance is merely one part of The Witcher universe. I don't see them making a romance DLC but I don't disagree with you and it wouldn't be hard to get people to prove they want it.
About the expansion maybe you are right but even if nobody voiced these problems. The context of there relationship during TW3 shows that her not showing up in the expansion would again probably not make much sense baring some "reasons". Honestly as I said above she should be a really big deal. Among other things showing the relationship during main quests and even in subtle ways an comments like Yen in TW3.
We will just have to wait an see I guess.