Alpha test of MAE filtering capability

Entirely agreed. On the other hand I have what is turning out to be a
    unique (here) point of view about this. I don't want to prevent this
    kind of theft -- I want to discover it, and remove perpetrators from any
    IXP where they try it. I don't want to block it. I want to ensure that
    it is never tried twice. I appear to be in the minority wrt this view.

This is a great idea. But do you have any idea how much expert engineer time
is involved in tracking down theft of this sort? Most of our employers would
much rather spend that resource on tackling the big problems.

If you can get the tools (simply having the IXP switch keep a port-to-port
traffic matrix would help a lot...), I suspect you'd find a lot of converts
to your "minority" view - many would prefer to expose and ostracize the
perpatrators of these thefts instead of ignoring them.