2/
I spend time thinking about how this (the importance of files and file data-formats) intersects with user-experience (UX).
For example, what types of files could you get regular people to create?
I don't think you can get regular people en masse to write JSON (including JSON-LD).
I think even getting them (regular people) to write HTML is difficult.
Something similar to Markdown probably has the best chance or success. Maybe something similar to INI, too.