Agreed on the "bit early" part, disagree on the "split". As for traffic, maybe it comes, maybe it doesn't; can't really make a call on that yet. I feel it's better to do this now instead of when there's 1000+ members here (if ever).
I wouldn't necessarily label it as a "split" instead more like an organizational restructuring to keep things slightly more focused and on-topic. One can choose to "subscribe" to Rust Lang + Rust: Support but not to the other ones if they aren't interested for example.