It seems like there are design ideas only. Are there any ideas about implementation like using some existing http servers or writing everything from scratch?
I recently threw together a quick-and-dirty prototype of this idea. It was an external tool which used the libmicrohttpd library to accept incoming requests, convert them to a SQL query (which called a stored procedure), and return the query results. (It allowed *any* content-type to be returned, not just JSON.) I only got as far as handling GET requests. The code is available here:
I'm also aware of an nginx module (ngx_postgres) that lets you transform requests into queries against a Postgres database, but it isn't "generic" -- you have to configure it for each URL that should be handled.