> As for the borrow checker thing, it is not broken but it's simply a limitation.

Limitations are when the borrow checker is not smart enough to understand things like sub-scope borrows (fixed by NLL) or the interaction of mutable borrows and loops (which hopefully will eventually be fixed by Polonius aka NLLv2).

But here they want to acquire a shared reference to an object with an outstanding unique reference. That is quite literally the first of only two rules references have:

1. At any given time you can have either a single unique reference or multiple shared references.

2. References must be valid.