Another idea: some sort of needs-based keyword matching? Scaladex' existing tag system is all about "what is this library good for?". For project-matching, maybe an additional set of keywords/tags for desired skills/projects? I'm thinking keywords like "benchmarking", "debugging", and so on -- general identifiers of what this project is looking for, so that potential contributors could filter based on the kind of thing they'd like to do.
Related: keywords for required skill levels, maybe? Amount of required Scala expertise in order to be able to contribute usefully? ('m just brainstorming here.)
Basically, I'm trying to put myself in the shoes of a new contributor, who wants to help but is intimidated by the sheer number of projects out there. How do we make it easier for this person to find a project that suits their skills and interests?
Oh, and from a purely practical perspective: if I'm a new contributor who wants to help project Foo, how do I actually contact the maintainer(s) of that project? That's a non-trivial problem, especially for someone who is new to the Git ecosystem, since GitHub provides no good way to directly contact somebody. Nowadays I tend to use Gitter, but not everybody uses that actively. This is, I suspect, a real and serious problem we might want to look at...