Think of building sites with Gatsby as an hourglass shape.
Gatsby itself is right in the middle. The wide funnel at the top represents the fact that Gatsby can take in data from all sorts of sources. The data could be in markdown files, from a headless CMS or some other API, from a hosted database, or pretty much whatever.
The wide funnel at the bottom represents that the output from Gatsby is static files, so those files can go anywhere. Netlify, GitHub Pages, ZEIT, S3, whatever.
Gatsby does a bunch of neat stuff (just the fact that it’s in React I’m sure is appealing to a wide swath of developers), but it seems to me the secret sauce is how it works with any data source.
If you were going to widen that hourglass shape into a, uhhh, pipe, you’d build a tool that connects arbitrary data sources with arbitrary static site generators. It appears that is what Stackbit is doing with Sourcebit. It has a two-sided plugin model (Sources: e.g. Contentful or Sanity; Targets: e.g. Jekyll or Hugo) with the goal of connecting any data source with any site-building tool that needs that data.
I would think contributors to all projects in both the data source and site builder arenas would be interested in seeing this succeed, including Gatsby.