I don't think that makes the complexity tradeoff worth it. This is the kind of tradeoff that makes the language implementation, reference and semantics more and more complex. Unfortunately Python has a lot of such complexities already. We don't need more of it. Such complexity hurts the creation of completing implementations.
IMHO programming language specifications and implementations should be simple and consistent so that competing implementations can be developed easily.
> people often using it subtly wrong?
I think that... you know... before writing serious software, these people need to roll up their sleeves and just learn the damn language. Just learn what references are and how they work in Python. It's not that hard. It is most definitely easier than adding a sphagetti monster to the compiler make it bend to the will of programmers who can't be bothered to read the tutorial. I mean this gotcha about references is taught in the 4th chapter of the tutorial. Can't developers even bother to RTFM these days before developing serious software with a programming language?