I don't see how any AE is going to really ever be properly "backed" by anything - you just end up with "centralised" Gateways a la Ripple or you end up with disasters like GLBSE.

Why do people think AE is so important when the only "decentralised" part is the "trading between IOU's and NXT" (anything else becomes reduced to having to "trust" whoever to actually respect the IOU)?