In case you have missed, there's 1.18 nightly builds: http://jenkins.ic2.player.to/job/IC2/job/1.18/space waves
As for open sourcing IC2 I also agree that some people (like me) might want to help fix bugs/upgrade to newer versions/add new things.
I wonder if this nightly build is stable? I'm still playing on 1.16 and really hope IC2 will soon have better support for new versions.