With the release of Revit® 2017 on April 14, 2016, the Revit vertical products Revit Architecture, Revit MEP and Revit Structure have been discontinued. Revit 2017, which includes the functionality of all Revit verticals, is now available as a standalone subscription.
Revit Structure in the Infrastructure Design Suite Premium and Plant Design Suite Premium and Ultimate has been replaced by Revit 2017.
Subscribers and customers with current maintenance subscription to the Revit verticals and suites containing Revit Structure have been migrated to Revit 2017 with no change to subscription cost.
For further details reference this FAQ.