From a competitive standpoint, Shadow Force is just slightly more useful than Dig. Actually, the pokemon might be able to pull off some semi-novelty stalling set if it got Mean Look, so...it's worth considering.
I really wouldn't consider Aura Sphere Lucario's signature move though, several other pokemon besides Togekiss have it. Darkrai got Roar of Time and Spacial Rend from an event, Spore used to be Parasect's signature move until Breloom got it, etc, so passing on "signature" moves onto another pokemon isn't completely unthinkable.