As someone who uses Reflex at work and has also written a bunch of Rust, I wish Rust the best but am highly skeptical it's going to be a productive tool, and not just nerd-fodder, for user interfaces.

Reflex is distilled mutation and week reference black-magic, and the safe interface it provides relies heavily on higher kinded types. Even if someone goes though all the trouble to implement it or something like it (And that would be cool!), I don't think the resulting algorithms can be packaged up in nice abstractions.

Rust is a great language, but it just shouldn't bother competing where GC will do. It's just no point trying to win a race with that handicap.

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I do believe in "one language for all tasks", actually. It's just that one language will have split ecosystems as it will support many idioms that don't interoperate well. Put another way, let's start with "multiple languages, perfect type-safe FFI", and then go for endosymbiosis.