A basic implementation could be a few lines of code, basically a fetch data and a serialization (here there is my very simple test).
A full implementation could be more complex because you can allow users to configure the plugin to search all contents, only a subset, the result of a collection, passing auth, also store images, etc..
Gatsby has 2 main types of plugins that do different tasks:
- collect data and generate graphql nodes
- generate a dynamic structure of pages based on node types
The first group is the one mentioned by Timo, and could be made as general as possible to cover every possible Plone query.
The second one can depend on the destination application layout..unless we wants to create also a general-purpose pages generator that "staticize" an entire Plone site with all the pieces (breadcrumbs, nav items, the entire structure, etc) and maybe a pastanaga layout.
IMO this could be a good project for gsoc but i don't know how deeply we wants to go in gatsby plugins creation.
I never get involved in a gsoc project, so i don't know if we need to find a project for the entire summer, for only one month or whatever..Probably a source plugin can be made in one month.
And to answer your last question: why not? it could be interesting, and i'd like to help Timo in this mentorship..but i have no idea of what does it means