Tfw you guys all believe that a character who is from the void century is some street level fooder
Imu will definitely not be street level fodder, but fact is that
Imu is more of a concept than a character. We know he is evil, we know he
has to go, but neither Luffy nor reader would feel much in terms of personal stakes when it comes to Imu. He is a rather abstract threat, even now when he has wiped Lulusia off the map... by contrast, stakes with Blackbeard are much more personal: he (indirectly) killed Ace, caused Luffy to nearly die trying to save Ace, and personally endangered multiple people Luffy cares about post-timeskip (Boa, Coby, etc.).
However, it also makes no sense for Luffy to face Imu before Blackbeard. Roger only learned the truth of the world after reaching the Laugh Tale... so it is likely that Luffy will go to the Laugh Tale first, become the Pirate King and only
then face the World Government. Unless of course current Vegapunk arc changes something, what with the guy being the foremost expert on the Void Century. Yet the fact that Luffy considers the Pirate King to be the freest person in the world indicates that the conflict against the WG will happen only after the Laugh Tale, seeing how the World Government is fundamentally opposed to the very idea of freedom in a way not even Blackbeard is.