We are currently evaluating EntityGraphQL in our project to provide GQL API for the existing data engine based on EF6 model-first with dynamically built EDM and Entity SQL queries. With some nasty workarounds we've managed EntityGraphQL to work with our data engine and now want to make things more smooth.

As our data engine doesn't rely on expression trees but instead on ESQL, the current implementation of ExecutableGraphQLStatement.ExecuteAsync() calling CompileAndExecuteNodeAsync() can obviously not be used. So there should be an extension point somewhere around that place to enable custom query processing.
As for now, we had to re-implement the entire ExecuteRequestAsync() in SchemaProvider, as the method (or better say the private one DoExecuteRequestAsync) is not virtual and also re-implement MapGraphQL() extension as the current one is looking for SchemaProvider service and not just for ISchemaProvider (that is actually quite strange, rendering a true service injection impossible).