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).