I highly doubt this was an intentional outcome. Multiplayer video games have had paid skins for years.
Fortnite has just attracted way way way more young teens, and they're bullying each other because of differences as they always have.
I wouldn't be surprised if there wasn't actually any more bullying going on because of Fortnite - it's just more obvious to people outside of the teenagers social sphere because of how wildly popular Fortnite is and how much media attention it's getting.
Maybe everybody should get assigned a random unique skin, but if you pay you get the skin you want.