Providing an avenue that students could (and almost certainly would) use to direct slurs at one another, seems like a surefire way to make things worse. I do share your concerns about social media.
Narrowing kids educational resources and knowledge in an attempt to stop bullying is a fools errand.
When I was in school, they'd just come up with agreed upon dog whistles and use them in front of you, directed at you. They'd usually be otherwise innocuous but packed with some alternative meaning only the in-group knew until they told you.
That's a lot less effort than learning an entire communication system.