>some x64 programs did adopt a convention to use shorter pointers, 32-bit pointers on a 64-bit operating system.

It's doable in managed languages, e.g. Java has compressed pointers by default on sub 32GB heaps. I suppose it's doable even in C alike setup (incl OS calls) but that would require wrappers to bit shift the pointers on each dereference (and passive to the OS, extern)