I'm curious – is MSFT using this in production, or is this a "20% time" project? I'm not sure MSVC could compile the GNU extensions used.

Author here. It is not currently in production, but it is part of a project in Azure which will go to production at some point. I'm actually leaving Microsoft next week and fully intend to keep working on it if I can reach an agreement to do so with my new employer.

> I'm not sure MSVC could compile the GNU extensions used.

The supported platforms only list Linux and Mac. Notably missing from that list is any of the BSDs (not counting what may or may not remain of BSD under the Mac hood).