IC2 has remained closed source for so much time. The community could help fix bugs & speed up the development of the mod. Also, deobfuscated ic2 jars are publicly available, what kinda exposes the source code. So why not go open source?
I'm guessing that right now they have "busy porting the mod to a newer version of Minecraft" as a decent excuse to postpone considering this. I realize we have no way to force them, but I'd be happy if they did open-source the mod after that, or at least post an official explanation of why they refuse (I've been unsuccessful at finding such an explanation previously posted).
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The original developer's thoughts on open-source:
As all of my projects, it will go open source if it's not continued by its orginial team anymore.
Which probably means: No, never.
I'm not familiar with the development so I don't know what (if any) contributor license they are using. It might not be possible to open-source the project without consent from every previous developer.
Note that IndustrialCraft (IC1), MedievalCraft, and Mine4Dead are still closed-source over eight years after being discontinued. I'm not sure if anybody has asked Alblaka to release the sources during those eight years, though.