* `?` can propagate values/short circuit control flow, but it also contains a hidden type conversion. The target needs to be a known type for it to compile.
* A proposed `catch` construct will include implicit type conversion for its result value.
Some things that came up in the past but met resistance:
* Removing project structure from in-code to being defined by the filesystem.
* Hiding `Result` types in signatures with special syntax.
* Dropping immutable by default, though this was pre-1.0.
Also, `Rc` and `Arc` are good examples for this. They do seem trivial, but having them auto-clone would mean:
* Every newcomer who writes `fn foo(val: Arc<Bar>) {}` instead of `fn foo(val: &Arc<Bar>) {}` or `fn foo(val: &Bar) {}` will get an implicit atomic increment/decrement at every function call.
* It also makes it a lot harder to reason about code if you want to use a clone-on-mutation-unless-not-shared strategy.