I was just poking through some of the code and noticed that there seem to a lot of open bugfix PRs [1]. Have you thought about going through and upstreaming some of them? Many of them seem like quick reviews.
Edit: Also, if you would like some help maintaining it, I imagine plenty of fellow HN-ers (including me) would love to help.
https://github.com/fogleman/primitive
Only the UI is closed source. It's written in Objective-C and basically shells out to the Go code.