My assumptions where MDF might be right fit are as follows:
MDF can be used as a Data Wrangling Tool by end-users
MDF is better suited for SQL Server-based Datawarehouse architectures to load the data into staging or data lake in clean format (prepare the data before loading it to SQL Server DWH and then use a proper ETL tool to do transformations)
If MDF has to be used for light ELT / ETL tasks directly on Data Lake or DWH, it needs customization for complex transformations...
My question would be:
A) Did anyone use Mapping Data Flow in production for option 2 and 3 above?
B) If assumption 3 is valid, would you suggest going for Spark-based transformation or an ETL tool rather than patching the MDF with customizations as new versions might not be compatible with, etc..