I see no problem with this outside of the set of core Rust technologies. If you were to require the average developer to type mathematic symbols it would be a barrier. However, libraries specifically targeting mathematicians would obviously not have that same barrier. Making mathematical equations clearer to read and easier to work with within that domain may certainly be worth using syntactic tricks and non-ASCII symbols.

I've seen plenty of code bases which are not in English, since the developers did not have English as their first language. This is usually a well-contemplated decision - for instance, the Ruby language source code is specifically written so that you don't require knowledge of Japanese to understand the core libraries or the C reference implementation.