Question about generic impls

foo.rs

trait SomeTrait { }

struct SomeStruct;

impl SomeTrait for SomeStruct { }

fn foo<T: SomeTrait>(_: T) { }

fn main() {
    // This works fine
    let x = SomeStruct;
    foo(x);

    // This fails with: error: failed to find an implementation of trait SomeTrait for &SomeStruct
    let y = SomeStruct;
    foo(&y);

    // If I add this to the code: impl <'a> SomeTrait for &'a SomeStruct { }
    // everything compiles. Is there some reason Rust can't derive that impl automatically?
    // Is there a plan to have Rust automatically derive it in the future? Does this have 
    // something to do with DSTs?
}