There are a number of plugins that use MySQL to store information.
Would be good if there was a plugin that'd let us query the SQL database and return the information via JSON. 
Would be great for building things such as Discord bots or stats websites.

"Would be good if there was a plugin that'd let us query the SQL database and return the information via JSON. "

Whats the problem to use native mysql?

Did you think through how you'd expect that plugin to work? (genuinue question)

Would the plugin try to host a web/'query' server that you could send requests to for fetching data? Would it talk to some other 'backend' server acting like some kind of proxy layer? 

I like the idea, not sure how feasible or easy it is though; If you used something like mongodb it could've been easier I'd guess, considering that is a nosql database (from my web backend dev. experience). You could always create procedures for whatever you need to fetch? 

I'd most likely just spin up some kind of backend server that connects to the same mysql host, I see no need for this to be a umod plugin tbh; just my take!

ninjasploit

Did you think through how you'd expect that plugin to work? (genuinue question)

Would the plugin try to host a web/'query' server that you could send requests to for fetching data? Would it talk to some other 'backend' server acting like some kind of proxy layer? 

I like the idea, not sure how feasible or easy it is though; If you used something like mongodb it could've been easier I'd guess, considering that is a nosql database (from my web backend dev. experience). You could always create procedures for whatever you need to fetch? 

I'd most likely just spin up some kind of backend server that connects to the same mysql host, I see no need for this to be a umod plugin tbh; just my take!

I've ended up doing just that.  Wrote a server that queries the SQL server directly using Sequelize :)