Be careful with terminology here when you say that something is simply not possible. The parent is asking about deadlocks, which includes scenarios such as entering an infinite loop or having a channel block on a message that will never come, and neither of these are things that Rust can guarantee will never happen. As I say in my sibling comment, what Rust's typesystem guarantees is the absence of data races, which is still an amazing achievement (unprecedented AFAIK) but is only a subset of the general category of race conditions.
That said, I wish they would have looked a little further outside Reddit's homepage rendering for parallelization inspiration. Reddit does not take a long time to render. However, CNN.com [which they looked at too] does, so...