Imu becoming irelevant would be like Joyboy becoming irelevant
They're the two most important characters, Imu is the final villain
Imu and Joyboy are indeed irrelevant, relics of 2nd world.
That's why Oda is speedrunning Imu and writing him out to replace him with those who are relevant - Blackbeard and Luffy instead.
World govt is turning into family feud between Figarlands, who probably were one of the 20 founding kings.
When WG is overthrown, leaving no single ruler, as it was intended to begin with, it will come down to Blackbeard vs Luffy over who gets to go to Raftel.
Buggy will also have his 5 minutes here.
After all that, we should get to the original sin - removing all devils(fruits) from the world and that's probably where the true final villain will show up.