I don't believe that it being written in Rust is a feature. The language it's written in is just an implementation detail.
It may be a good example of programming that's worth reviewing as I learn or it may just help provide a sense in the kind of community that's growing (or not) around something that's relatively new (in some stable status at least) like Rust.
Had it not said "Rust" in the title... I may well have not bothered to look at this at all.
The choice to start a new editor in Rust signals to me that this editor won't have as much trouble optimizing for speed as other recent editors, and it also signals that it may be able to hook on to recent Rust energy to get collaborators. To the end user, that potentially means speed and longevity.
Whether rust is beneficial to a text editor project is up for debate (my guess is no), but I agree that language is a feature of an open source project in the types and quantity of contributers it attracts.
The implementation of Xi, has some novel things that might interest Rust programmers, like a practical Rope implementation, which are quite rare in Rust and often abandoned.
I was interested in Rust before, but it now seems like Rust programmers are like vegans (I have to hear about it every 10 minutes.)
I'm not saying anything specifically about this case, because clearly the information here is very limited, but there is a case to be made for rewriting projects that work to increase maintainability in the future. Most newer languages do have an edge in this department, as they are more conscious of those issues.
There is sometimes the benefit of a rewrite regardless of language, as well; cleaning stuff up, organizing stuff better because you now know better, etc..