Apigee is the Gateway
Not Middleware or Integration framework nor for replacing such U.C
Understand that Apigee can do the SOAP to REST or REST to SOAP conversion, but is not replacement to ESB or Message Broker, which involves complex transformations for Legacy modernization.
There are other value adds to Gateway, but correct design would be to have the ESB or Message Broker do the Integration and ETL handle the File or Batch process. Apigee is more Async and Realtime.
We understand that On - Premise Apigee can process the max of 10 MB of File enabling the Streaming and without usage of any Policy, which would require processing the Data for Stream enabled Use case.
When it comes to above U.C, scenario I believe we should continue doing such enhancements in ESB/IIB/ETL.