Maybe GraphQL can be your savior?
The problem is generally not the surface language, but the underlying distribution/querying mechanism.
It is, of course, possible that SQL is too complex a language for this dream.
GraphQL is just a language much like SQL.
Yes but it provides a standardized way to deliver a unified interface to query your data, which is what OP is after?
“With high throughput and low latency” are the operative requirements for OP and GQL doesn’t help with either on its own.