More and more chances of Teach being the final villain rises....

Imu is a common enemy to every ppl.
Pirates, Marines, RA, civilian etc
Biggest obstacle and too powerful for any single individual, so various factions will teamup to take him down
After that the throne will be empty for anyone to take it so, the actual final battle will happen after Imu demise.
Kinda the way the story will be moving i suppose...