I would just write the world in a way that is interesting to you, and add to it as players show interest. “Hey, I want to play a Tabaxi” -> “oh okay, let me think about what that means and I’ll get back to you.” This also gives you more latitude for using their ideas to inform the world. “I want to play a Tabaxi Wizard” -> “oh interesting, maybe there’s a clan of them that…”
You’ll be able to focus on what you care about, which will make the world more interesting, and allow players to incorporate things they care about if they wish, which will make it more fun for them too. Framing it in terms of “up for deletion” implies you need to answer everything about the world from the start, which is not only inefficient but an impossible standard. Just because you haven’t considered something doesn’t mean it can’t exist.
I don’t know if there’s a service that provides both functions. I’m sure there’s a way to do it - Lemmy posts are already accessible through Mastodon. Currently, I assume you would need the instance itself to offer both services under one account.