That said, why limit yourself to Rust specifically? There are plenty of other languages with "fast enough" implementations/runtimes, which also promote "higher quality software by default" but also don't require manual memory management.
Maybe the limiting factor is availability of good GUI toolkits? Or do text editors need particularly low level control over memory in order to avoid performance issues?
* The language you use defines how you attack the problem. If you use Snobol then you can only think of the world as strings. If you use an APL derived language then you think in terms of arrays. * If the language's core attributes really suit the problem then you get something fundamentally different. We see this with Erlang which achieves safety but (finally) acknowledging that stuff crashes so build support for recovery into the language.
As someone who used to commercially sell a text editor derived product, memory management is just plain hard.