It's coming very soon (tonight/tomorrow). The reason the Steam patch hits a little earlier is because I can very quickly update that Steam version and push an update to all users, so if I miss something big in a new patch that needs to be corrected asap, I can do that right away. I've had a few (smaller) cases of this during the last few days that I wanted to fix before making a new installer version, and have done so.
Would love to be on GOG, I did inquire before the game's launch but they had too many titles in their schedule for the month ahead at the time. Hopefully in the near future!