Davis is one of the best fighters in the world, but Inoue is currently the best fighter in Japan. As long as Inoue continues fighting in Japan, he won't achieve the same level of popularity that Davis enjoys. Although he is currently the top pound-for-pound boxer according to records, he will not be in the Hall of Fame if he doesn't take bigger risks and push his limits.
Tank Davis could move up in weight, but he might end up like Pacquiao due to his height. Honestly, I don't see him being better than Pacquiao in his prime, so he might not move up much and will just stay in his comfort zone.
But aren't both of them currently in their comfort zone, they are still trying to hunt for title by moving up to class above it so it is very likely that they will face new challenges in the future.
For Inoue, it is clear that he will develop well if he can get what he wants by moving up in class, but meeting Tank Davis will take long time and it is impossible for Inoue to immediately increase his weight significantly and fight Tank Davis.
But yes, we see what will happen in the future, it clear that right now they are the best boxers who both always win in every fight.
To be honest, he hasn't done anything yet in the 135 lbs division and what others have said, he is a paper champ here. He didn't face Haney at this division, and then we have Shakur and Loma still lurking. Loma is a regular champion now and so there is a chance that Davis could step up and fight Loma or even Shakur. And in this fight, he weigh in at a slim and trim 133 lbs, so meaning he can still make weight here and probably have time to make it in the next coming years. And I don't think that money will be a problem as for sure there will be a lot of promotions or even the Saudi to cover for this big fight if Davis wants it.
But at least there is an opponent he will face in the future, I sure we all know what Bob Arum said about Tank Davis and who Tank Davis next opponent will be, we might see more interesting fight than waiting for Inoue to catch up in weight his body to match that of Tank Davis.
There is lot of discussion and news circulating about Tank Davis and Inoue, but we can't find clear point regarding certainty about either of them, I think what Bob Arum said will indeed happen in the future.