This is good but one obstacle in the USA is how to get funds into the other person's bank account. Chase is already making it so you are not able to deposit cash into someone else's account,
By normal wire perhaps ? Wires aren't blocked AFAIK. Only direct deposits.
Collateral should be greater than amount in exchange. If they exchange $1000 for 1 BTC, collateral should be 2 BTC. So when Bob receives $1000 it's cheaper for him to unlock collateral (2 BTC) than to keep 1 BTC worth of product (cash in this case).
Collateral can obviously depend on the trust level between participants and other parameters/circumstances.