The Official Dash Roadmap can be found at https://www.dash.org/roadmap/. Previous versions can be found in the history of this Git repository.
The most recent version in this repository (which is now superceded) can be found here: https://github.com/dashpay/dash-roadmap/tree/eb7f6bf4c0700fd2568a22b9a0b97881c55fe4da