HN user
I think the things that make Rust safer than C++ make it look more like a functional programming language than C++. The main point is that there are some influential people at Epic (SPJ has often spoken favourably about Rust) who would favour it over C++.
I suspect the use of Rust rather than C++ might have something to do with the fact that Simon Peyton Jones and Lennart Augustsson (both of Haskell fame) both work at Epic and there would have been a strong internal push to do this in a language with some functional programming features. Rust rather than Verse because that would probably not be the right tool for the job (even if Simon works on it). Rust rather than Haskell probably because of performance -- DARCS never caught on partly for performance reasons.
Characters can be grouped according to the stroke count of their radical and phonetic components. This allows one to have a list of characters, and enables one to look up characters that one hasn't encountered before (although nowadays you can also use a Chinese ocr app for that purpose).