Mari0 SE, the upcoming update that adds online play to the game, does not have a release date, and that’s simply because it isn’t done.
To be more precise, the online mode is proving to be tougher than expected and we can’t tell when it’s going to be done. Since this is the most anticipated feature, I do not wish to release the game without it. If something like the overworked Portal campaign wouldn’t be done yet, I could release the game without and then update again when that is done, but it’s simply not an option for me with online play.
I hope you understand and thank you for your patience! It’s your constant positive feedback that keeps us going.