I think what you esssentially want is a language with a powerful effect system and substructural typing, along with regions for memory management. This is like

I think what you esssentially want is a language with a powerful effect system and substructural typing, along with regions for memory management. This is like what Rust does with ownership semantics and the borrow checker, where normal types are linear/affine, that is, they can only be used (exactly,at most) once. What would be more powerful is having some effect of GC'd function, and some effect of non-GC'd function, and you can only pass the barrier from GC to non-GC if it's a linear/affine type. But when you're in a GC function you can use whatever types you want to. So instead of being stuck with the borrow checker, you can just decide at a drop of a hat to enter GC mode to write your linked list.