I’ve already volunteered for the Javascript SIG, although I’m also willing to contribute some time to the Core SIG work as well. I’m fairly familiar with working in nixpkgs, having contributed a few patches to it in the past, and after having daily driven NixOS for a few years… you get used to reading Nixpkgs source code 
I’ll also link my post in the JS thread as some examples of work I’ve done in the Nix space.
At the moment, I’d like to focus primarily on the Javascript SIG work - but I imagine the core is going to be a pretty high-volume, high-effort stream of work, so I’m more than happy to help contribute a few things here and there as well.