That's a very strange idea: JSON is basically structured data, like XML, it's nice for documents with deeply nested structures.

The main issue is that contrarily to a DB, any modification will shift everything after it, so any indexing will have to be corrected. I suppose that if the document is not stored as is, but instead broken up in pages (filesystems are likely doing that already, so piggy backing on that could help), then indexing could be improved, but then storage starts to look like a regular DB, rather than JSON.

Interesting nonetheless, time will tell.