Roadmap / Github project?

Is there a Roadmap and/or a GitHub project for Workplace Search?

For example, I'd like to know what other content sources are planned, or what additional features we can expect from the custom content source.

There is not a publicly available github repo at this time. And there's not a public roadmap, to my knowledge. If you have a support relationship with us, I'd suggest that you file enhancement requests for any content sources/features that aren't currently provided.