> "Linear reference counting is an elusive concept, where we can completely eliminate the counter integer, and do all of the reference counting at compile time."

Right. I've occasionally thought about that for Rust, as a way to do back references. You can have an Rc owning an object, which can own another object, which can have a weak RC reference back to the original. This allows you to find an object's owner when needed, so you can do inheritance-like things when you need to. The single-ownership and dangling-pointer checks are made at run time and will panic if they fail.

Now, the question is, can you statically check access behavior and determine that those panics will never occur? If you can, you can eliminate the reference counts and checks. That looks 1) possible, and 2) a PhD thesis sized problem.