If you want to do something, just do it. Its up to you what you do and what you don't consider to be doable or useful-enough to be done. We are not ones capable or supposed to tell you what you should or should not do with your spare free time on your project.
It seems that this system would simplify and quicken process of upgreading items of players. Why would anyone not want to have such thing and preffer more cumbersome, difficult to search through and use system? Just make sure that it works for all items its needed for, that it doesn't have any bugs and that players can see what will their items look like after upgreade, should their display change in any way (if not, you don't have to worry about the last part). As long as you can provide that - noone would preffer 20+ NPCs over 1, which is even quicker and more easy to use than any one of those original 20 ones.
Blizzard doesn't give a shit about private servers, as long as they aren't really huge (dozens of thousands of players online) and/or aren't making abudant amount of money from their game. Servers Blizzard pays attention are ultra rare and are not determined by features, but by scale. You are fine.
Last but not least, every single piece of job well done in your portfolio increases your chances of getting somewhere. Just note that for me as former leader of multiple projects, and I know that other admins are usually the same, is always more important what kind of person is applying for position in team. Its personality, attitude, will to learn new things and get stuff done (reliability) what really matters the most. When someone wanted to be GM on any of my projects, I never cared (much) if they never had ever worked with even stupid MySQL databases before. But I cared a lot if they looked like jerks I wouldn't want to work with (or which would drag server down by their attitude towards players) to me - you know, noone want to work with people, who are not nice. Especially when its a hobby, personality can matter way more than any kind of skill.
So, if you are a cool and nice person with friendly attitude towards players, good teammate, responsible and reliable guy, willing to learn new stuff - thats what you need to be if you want to get and keep GM position without any issues. Everything else is just... something extra. At least as long as admin you want to work beneath is a sensible person. This is hobby, its about having fun and letting people have fun. Thats why attitude matters. Not some... slugfest of technical skill.
