Respectfully, the current webpage and explanation don't provide enough detail to entice me to join the waitlist.
My thinking is this: everyone has their own repository of useful resources, divided into categories, languages, etc. The public v. private question is a good one: my initial thought is to give users the choice to do public _or_ private. This will let folks create code snippets that they'd rather keep private and share others that they're interested in sharing.
As for collaboration, I think I'd rather divide this up into discussion collaboration (comments, namely, and maybe code-level comments on snippets) and code-level collaboration (like contributing to a piece of code with a Git-like PR), so that users can choose how they want to interact.
I want to re-clarify, this is an idea still in its infancy, so if there's something you'd like to see, that's the real purpose of this post: to get a feel for what folks would like to see, so I'm not just building something for myself.