I have many great ideas for WoW, related to Cosmetics and game design in general. If I worked at Blizzard, I would love for my suggestions to make it in to the game, but probably I could not decide on them all by myself, since it’s a company, and not determined by decision of a single person. In fact, I would appeal for a Job in Game Design department, if they did not require like 10+ years of experience in Programming etc. 
You can read my own threads for my other great suggestions, but they are just some of them. I thought of many great ideas before, and I submitted those in-game several times, hoping to see that they would make it into the game one day. However, Once, I had made a suggestion for a new Phoenix mount, and I had stated that, it could be even a Store mount. And they had added Sapphire Skyblazer after some time, which resembles the mount I had suggested before, so it made me happy to feel like Blizzard listened to my Suggestion to some extent 
. You can find the Phoenix that I suggested for WoW in this video, it was a while ago,
I’m not sure if the video link is still up though. However, you can search for “Türkiye Vakti” video on the Youtube. If the video is still there, you can find it and you can compare the Phoenix in the video with Sapphire Skyblazer mount.
From my own threads where I posted some other great suggestions. You can read all of them in the link below.
One of them is; allowing Hair to be shown with Hoods. Like Sylvanas Windrunner and Valeera Sanguinar and some other prominent NPCs. I think if they add new compatible hood models, it would be possible.
Also, it would be cool if they add recolors of Sprite Darter’s Set, in different colors like Red, Yellow, etc.