Wow. Lots of arguments for a perpetual fee. See my post above for avoidance of such.
So replace a tiny fee for a much larger one? Even if the system is feasible on a large scale (unlikely), there will still be counterparty risk. You are trading direct counterparty risk with the risk of the assurance entity. Still from a fee standpoint it would be a massive step back. Your third party reinsurance entity isn't going to take risk for no gain. Their reassurance fee would have to cover the costs of verify entities, establishing their credit worthiness, protecting against fraud, and covering the % of transactions which are defaulted on. Fees are very low 0.1 mBTC per KB. On a 1 BTC transaction that is 0.01% of transferred amount. Can a third party reduce that cost significantly? I would say no.
Bitcoin fees are very low 0.1 mBTC per KB. On a 1 BTC transaction which is under 1KB that is 0.01% of transferred amount. There are a couple of things which "could" reduce this further in the future.
Currently miners ranks fees by the ACTUAL FEE / ACTUAL TX size. The client however rounds up to the nearest full KB when paying fees. This means that a user interested in minimum fees is overpaying what would be required by a miner with the same requirement. For example say a typical miner requires a fee of 0.1 mBTC per KB and fees less than that are treated as non-paying. With average tx being 600 bytes this means a fee of only 0.06 mBTC is needed (0.06 mBTC *1000 / 600 bytes) to be above the 0.1 mBTC threshold required by the miner. Right now the client would round the 600 bytes up to 1KB and add a fee of 0.1 mBTC to the tx which is 0.04 mBTC more than required. From a miner's perspective the tx has a fee of 0.167 mBTC per KB.
The client should be modified to make the fee paid based on actual tx size not rounded up to the nearest KB. Miners already use this methodology for ranking tx for inclusion in the next block so it makes little sense for the client to use a different methodology when deciding on the fee paid.
The fee required for relaying by v0.9 nodes has been reduced 90% to 0.01 mBTC per KB. The client doesn't yet allow paying a fee that low (when a fee is required). This is done intentionally to ensure that when the client does allow that there will be enough nodes which will relay those tx to avoid them being "stuck". Future versions of the client will also allow creating at this reduced fee level.
If you combine those two changes it would reduce the fee required to relay an average 600 byte transaction to a mere 0.006 mBTC (600 sat) or roughly ~0.3 US cents per tx. Now relaying doesn't mean a miner will include it in the next block. Some (or significantly all) miners may require a higher fee however those two changes will for the most part take the client and nodes out of the fee decision process (with a negligible mandatory requirement on low priority tx to ensure the network is safe from DDOS attacks). It will be important for miners to be more open with their fee requirements so that users can make a better decision on what fee (if any) to pay.