That's sort of what I had assumed they would do, originally. I still haven't seen any of my backer DLC, because I backed for the physical PS4 version, but have never owned a PS4. I was sort of hoping they might offer the backer DLC for purchase with these new PC releases, despite the backlash it probably would have caused. I'm not sure of this, but I wonder if it was something they were obligated to do by the distribution platforms; Like, even just setting a flag constitutes a 'download,' requiring a DLC code, or something equally stupid.
Although, now I'm actually curious if they are in the game code, and just need to be enabled, like Shenhua's alternate outfit, and the Merry Cruise prizes. I wouldn't have done that on the Epic, or Steam versions, but the GOG version is DRM-free. So, really, there might not be much restriction on enabling them for that release.