My advice would be a "Blended Approach" based on "Self-Service BI " & "Corporate BI"
In the "Self-Service- area" the business is in the lead down to individual datasources.
In the "Corporate-area" IT is in the lead up till Datamarts.
Based on Report Life Cycle management valid reports will transfer from Self-Service-area to Corporate-area.
Hope this short explanation is clear.