Pluggable GC heaps or the like will likely become possible in Rust at some point. We can already see some of the groundwork being provided, e.g. with support for things like custom, user-specified allocators (at a local, not whole-program level - this is not yet in Rust, but definitely in the pipeline!)
It's just a bit silly to couple one's choice of language/ecosystem/etc. to a single memory-management strategy, and the Python/Nim-like choice of obligate GC as an extension to obligate reference counting also seems a bit puzzling. That's basically taking every sort of automated memory management under the sun and compounding their disadvantages - I'd think one can do better than that, in fact even Go or Ocaml do better than that!
It's just a bit silly to couple one's choice of language/ecosystem/etc. to a single memory-management strategy, and the Python/Nim-like choice of obligate GC as an extension to obligate reference counting also seems a bit puzzling. That's basically taking every sort of automated memory management under the sun and compounding their disadvantages - I'd think one can do better than that, in fact even Go or Ocaml do better than that!