co-op won’t be added anytime soon
Co-op mode requires money and time to be done (~3 months only for the base, from what iA said, without any kind of updates during this period). It’s not the main priority right now. In-mission multiplayer may appear later, but very likely not before the game is released, nor shortly afterward (mobile version comes first).
Multiplaying
https://youtu.be/ZzYRPixc5e0?t=3976 1:06:16 (iA’s explanation about the multiplayer situation).
i can’t quote