What is the scenario you're imagining of Alice attacking Charlie?
What you want to do is an digital version of Hawala. Hawala works, but there is a reason it is not automated. You can not scale it and it gets very easy to hit liquidity bottlenecks.
I think your ideas are in the right place (if you look at Raiden's off-chain side payment channels, it works somewhat similarly with what you are attempting to design) but can we agree to the fact that if they were feasible to be done without BFT mechanisms, it would have been done already? It is not like people want to use blockchains.
What are these liquidity bottlenecks? Feel free to reply with a link or a keyword if this is common knowledge.
One thing I like about this model is that you can have regular fiat money on top if Charlie gets his IOU from the US government and Alice gives one of US government IOUs back. But it can now be a single network for all currencies where anyone can start issuing their own money.
> can we agree to the fact that if they were feasible to be done without BFT mechanisms, it would have been done already? It is not like people want to use blockchains.
I'm not sure. Would anyone be able to profit from it? Developing the software and educating people is hard, especially with p2p things.
Re: profiting from the Blockchain, you are going at this backwards. You don't need to make it profitable by the tech. What we want is to have a global payment network that can make transactions cheaper than (and equally faster/secure as) Visa. If that were possible to do without blockchains, the market would pay handsomely.
Another thing, if you want to make transactions like the one you described, you don't need to pass IOUs around, you just pass money. Alice gives the IOU to Bob, Bob gives her money and then she can buy from Charlie, David, Eve or anyone else.