I wondered if you could put the source code with the game. I believe this would be great for everyone involved. Let me explain:
There is an active modding community and this would make it way easier to write modifications for the game.
There are a lot of players already from the FOSS community. I think if you give the source code with the game, this would make the game very interesting for people who don’t like running closed-source software on their machines and for people who like modding games. This might not be a very important reason for you, but I think the game could gain a lot of popularity in this community.
I know a lot of people who like the game and are also developers, so if they find a bug they might be able to fix it themselfs rather than needing to open an issue. They could send the patch via git-send-email to you.
This will probably boost the sales rather than encourage pirating: This is a move that no game at this scale has yet pulled of (I think). I am not saying this will be in mainstream media or on the hacker news frontpage (though that would be cool) but I mean this will probably attract a lot of attention for the game. There are already ways to pirate the game.
Please note that I am not demanding that you should release the source code. I just want to friendly ask for it. I don’t mean you should make it open source, source-available would probably be best.
ps: Please excuse my English ;-)