There is no official standard of requirements for having your number retired at ISU. There isn't now and and there hasn't been in the past. So trying to use the imputed standards of one honoree when looking at another is a fool's game. Each potential honoree must be assessed in his own context.
The choice to retire a number isn't a matter of checking boxes and declaring a pass/fail, it's essentially a political matter where the only people with votes have be to lobbied and convinced that it's appropriate. The people expected to have votes, in this case, are the Head Coach in his capacity as administrative director of the program, the Athletic Director, the University President, and some collection of other figures including inputs from the Faculty Senate, the ISU Foundation, and the Alumni Association.
That all being said, I believe there's a case to put Melvin Ejim into consideration for the honor of having his number retired. His athletic accomplishments have earned him multiple entries in ISU's leaders lists including most games started, most games played, and 2nd most points in a single game as a sampling. He earned Conference Player of the Year honors and an All-American team placement. His on-court numbers are good enough to start the conversation.
In addition, he is set to graduate Cum Laude, and has earned a number of academic awards including Big XII Scholar Athlete of the Year and 1st Team Academic All-American honors. Ejim has exemplified the ISU ideal of a STUDENT-athlete.
Finally, Melvin committed to play for ISU at a dark time in our basketball program's history and stuck with that commitment even after having every reason to reconsider and opportunities to play elsewhere. He made an affirmative choice to come to ISU when he had no obligation to do so. In so doing he became the first four year player to graduate under what we all expect to become a new generation of greatness in ISU basketball. He is a foundation stone for all the other work Fred Hoiberg has done to revive our great basketball tradition here at ISU.
I believe there is a case to be made to honor Melvin Ejim by retiring his number. That case deserves to be presented to the makers of such decisions.