Re: I think it's a reasonable idea.
Directional? Triangulation. Over time, too.
Now things might get a little hairier if the program could be run on a network (writ "large, ad-hoc") of other devices, voluntarily or otherwise, with central reporting... At the very least, running something like this, provided the list of stolen MACs is available, it can be used by ne'er-do-wells to shake down a possible device-thief. But no one's about to complain in such a case *cough*.