My initial goal was to develop a tool that (1) used a domain-specific language to describe computation (2) was actually used in production. I did not want a proof-of-concept as one of the major arguments for developing a domain-specific language (DSL) is that it is more usable than just doing a traditional library in another language. As I am skeptical that you can fully evaluate how good a tool is without long-term, real-world, usage, I wanted NGLess to be used in my day-to-day research.
NGLess has been a long-time cooking but is now a tool that we use every day to produce real results. In that sense, at least, our objectives have been achieved.
Now, we hope that others find it as useful as we do.