This whole promotion thing is stupid. Let's say he was promoted.. so? How would this change his character or the stories about him? It would change nothing. He would just have one more pip.
It gives the character a turning point and by doing something awesome to earn that promotion, it shows that he is putting effort into improving himself and making inroads into showing the crew what he can do. It is a reward for him that proves he has the right stuff. Who wants to see a Ensign that stays that way for 7 years, it makes him look like that pathetic version of Picard from Tapestry, that he is a loser with no real drive or initiative, audiences don't want to see a character who is not proactive.
Really, how it would have hurt Harry Kim as a character, if he got a promotion? I think that would give him a place to grow and develop rather then staying stagnant as an Ensign for 7 years.
The toys would be incorrect. Why buy an out of date doll? The Janeway dolls from season two are still selling, but no one wants to buy an Ensign Kim doll when there's Lieutenant Kim figurines in the next expansion... And if the character is so poor selling, and if he is likely to get another promotion making the new action figures not out yet autoredundant... WHY BOTHER MAKING KIM TOYS!!??
Examine how ####ed up the TNG season 2 novels are.
Pulaski put the poo into Pulaski.
It's an exhausting aberant detour that no one should bother with becuase Beverly is coming back and came back and put a ring on it.