Audioholics has
this article about in wall ratings and NEC restrictions, which may help a little. If the "future speaker wire" is bundled with live electric wire (at any point in the run), then both from a performance and code perspective it shouldn't be used.
In wall wiring is typically CL2 or CL3, which more than anything denotes a safety threshold; "shielding" from interference isn't usually addressed in manufacture, and the NEC requires minimum distnaces between the wires anyway.
I have all of my in wall spkr wiring separated from electrical by at least 1 wall stud (16"), and intersects in the attic at 90 degree angles, as recommended by an installer.