Don’t want to make you sad, but probably never. Because of three things:
- Game was not designed to be with mod support. Its internal structure is not really intuitive.
- Up until 5 DLC there was no mention that game will even have Steam mod support. Devs saw that people ask for it to be able to prolong the game’s life and eventually developers decided to release another update to include Steam Workshop.
- GOG is not so big community and doesn’t have dedicated platform for modding, so it is really unlikely that developers will afford more time to make additional updates for more easy modding on EGS or GOG.
And to not look like a Steam fanboy - I also have my copy of Phoenix Point on the GOG.
Maybe this will help a little: