I've gone through and cleaned up all the references to it in our docs and marketing, so we stop misleading people with this notion.
As we wrote more and more Rust, it became clear that unique ownership (~T, now Box<T>) was just as useful, faster, and better. Remember, this type basically compiles down to a regular pointer, with compiler inserted malloc/free. So you can imagine how much less that is compared to a refcount + cycle detection.
So, Gc<T> was never really improved, and it's usage in the compiler itself was less and less. The last place it was used was in the AST, and so syntax extensions used it, but we didn't recommend it for anything else.
Now, this past week, a contributor managed to re-write the AST to not use Gc<T>, so even than is gone. Or will be soon, I forget if it's passed CI so far. But anyway, now that it's gone, it will probably be simply removed, though that decision hasn't been made yet.
Basically, what it means is that affine types are awesome.