Definitely a day 1 purchase for me as well, no other game has the same amount of love and polish as Factorio does, both when it comes to the vanilla game and mods, and I know they will deliver a good experience with the DLC as well.
However, I am worried if it's gonna be enough to stand out among other games in the genre. It has been many years since Factorio last got a substantial content update (maybe too many) and in the meantime we've got a lot of similarly-genred games like DSP or Satisfactory that have raised the bar in areas that Factorio lacked. I hope F:SA has enough meat on its bones to substantially change the core game rather than just more of what we've already played.