Haven't read the entire thread so I dunno if someone has said this already, but The Witcher 3 uses a variety of 3rd party middleware and I am not sure if it was (or is) all available for Linux, so if they want to or plan to do a Linux port of the game they would most likely be dependent on whether or not their 3rd party middleware suppliers make their software available for Linux also.
At one point I did research on various middleware used in TW3, and at least all the stuff that's officially listed by the game (in credits and etc.) is available on Linux. Developers never said they were blocked by middleware, but on the other hand they said practically nothing to begin with so who knows what is blocking them.
I suppose the main blocker is lack of professional foresight of their management (not of developers, but of their bosses). If they wanted to make a Linux release, they should have paid attention and worked on solving these issues from the start, instead of waking up late in the process and realizing it's a monumental task because of all the issues they didn't anticipate lock them into certain platforms.
We'll see if they learned from such major mistakes in Cyberpunk 2077. So far I'm not confident that they learned much. They didn't share any info (about wither they use Vulkan in CP2077 for example).