User blog comment:B214/Question and Answers 2/@comment-187.209.0.247-20140226163658/@comment-24501441-20140226170511

Not sure what the authors intentions are, but I think it's reasonable to expect that if he were to become a high class devil, it would be near the end of the series. You have to remember that Issei hasn't even been a devil for a year yet. As a devil he has thousands of years to make his dream come true. There is no rush.