If we believe Oda then, only one of the following is possible:
- Blackbeard is the final villain and Marines/EG/Imu gets done in by Revolutionaries.
- Imu is the final villain and Blackbeard's arc will be significantly small.
Either way, Oda has to cut off one of them for the ~5 years timeline to work.
Since Imu was a late addition, I guess Imu will be axed.