This would allow us to have a FIXED value e-currency which we can use for micro payments.
It won't be fixed at all if the issuer suddenly stops redeeming their IOU's and in if fact such IOU's will quickly become worth *nothing* - as you said the Asset can be anything including "Pirate Ponzi Coins".
Understand that just calling something NXTUSD does not at all make it worth 1 USD - it's no different to Mt. Gox USD amounts (they have clearly been valued at less than *real* USD amounts for a long time).