He really carried that monicker, as the "Monster" because of his power behind those punches. And it's now being magnified after knocking out one of the legends in boxing. And then send signals to other bantamweights and even to the next weight class although that power will have to be check if he can carry it to the next level or not. I guess life imitating art here, we all know that there are Japanese anime about sports, i.e basketball boxing and others and maybe there will be future Japanese character similar to Inoue, 
With Bob Arum as his promoter, expect Inoue to conquer the higher division just like what Manny Pacquiao did in his prime but of course with the help of Bob Arum. Maybe his fight with Butler if pushes through will be his last in the bantamweight division and then move to the 122 lbs limit and see what the future would give to this Japanese superstar.
Seldom we can see a Japanese boxer who dominates like Inoue so i think they will also pay tribute to what he did by imitating his life with an anime hehe.
I agree, with Bob Arum's experience, Inoue can be the next biggest star, although we can't compare him with Manny's enigma and charisma though. But Arum + Pacquiao at his prime? they put a the blue print, on how someone from Asia conquer the boxing world but carefully nitpicking their opponents. If we look at Inoue's pics in his latest fight, you can see that he has a broad shoulder and his lats is huge and it can still expand a bit. So definitely, once he is done with Butler, he will move up to 122 lbs. We have Fulton (WBC/WBO) and Murodjon Akhmadaliev (WBA/IBF) waiting for him. But we might see a unification fight between the 2 as they shared all the belts.