A comment from the author /u/ClayTownR on reddit:
The original reason I got into garbage collectors (a long time ago, and long forgotten now) was that I was implementing a runtime for a scripted language. When I originally wrote it, I had to do some manual finagling with weak references to ensure that I didn’t leak any memory.
In general, the main uses for a GC in rust would be interpreters for other GC languages and working with graphs.
It turns out that graphs are really useful for UIs, so hopefully this makes stateful UIs nicer to work with.
I miss the early days of Rust that included GC’d types.