Rust supports proc macros, you know-- you can do literally anything with your code. So what you describe is already possible! Make a good proof of concept and submit a proper RFC for it, and it might even be adopted as part of Stable Rust!
Yes, that is exactly my intention, for the majority of code this compile time reference counting is good enough.
You can of course use Rc types in Rust, but that is verbose, and throws all ownership out the window, unlike Lobster.
I think Rust should allow this kind of relaxed ownership, with ARC behind the scenes, as lots of user level code should not require fussing over ownership details. A "get shit done" mode.