Due to circumstances in my life, I need to finish this game soon. I've decided on May 31st as the target release date. What this means is that I will focus on the gameplay mechanics and making the game playable. It may mean that there may be only four races to play with (there's a new one in works), weak AI (the support for AI scripting will be there though), imbalanced technologies, and not many sounds/music at release. However, they are all contents that can be easily tweaked and added without altering the game's code. All the gameplay features that I discussed (stacked/single ships for example) will be implemented by then!
I plan on supporting the game after its release, by improving the AI, adding new races, balancing the technologies, bug fixing, etc. But those requires a lot of players' feedback, so I guess you could technically say that May 31st will be the end of the Alpha version, and the Beta testing has begun. However, it will be a full release, because it will be feature-complete, and people can mod the data.
That's the plan, I'm going to try and finish up the game before May 31st!