I don't know why you're calling all of that stuff "weird". I have to assume it's simply because you were never exposed to another language that had stuff like it. But you're definitely wrong about that keeping Rust from going mainstream - just look at Swift, which has a very similar trait system (called protocols), enum variants with associated values, an arguably weirder error system, widespread closures, and half-functional style. And I'd say Swift is already fairly mainstream.