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You should only trust gateways that have earned your trust, likely through frequent audits of their assets and liabilities. And that includes IOUs issued by other gateways. Note that gateways could accept IOUs issued by other gateways at less than face value. The exchange rates between the various IOUs for the same currency issued by different issuers would be the best market estimate of their relative reliability.
So lets assume all gateways only redeem their IOUs (because people would be silly to use a gateway exposed to risk you said).
It's likely to start that way, unless some very widely
trusted banks get in the game.
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Oxymoron spotted! I think you're preaching to the wrong choir buddy.