SpaceX will no longer divert resources to make the Falcon 9 second stage reusable. The second stage modification for a mini-BFR will enable low-cost testing of the BFR upper stage.
SpaceX will shift all development resources towards the BFR by the end of 2019. SpaceX is currently spending on the crewed Dragon.
Btw, SpaceX is no longer planning to upgrade Falcon 9 second stage for reusability. Accelerating BFR instead. New design is very exciting! Delightfully counter-intuitive.