If merchants can avoid 3% credit card fees by giving you a 2% bonus if you use bitUSD, thus saving 1%, then you might get a 2% bonus for using bitUSD.
If you get a 2% bonus for using bitUSD, you might be willing to pay 1% premium to buy it.
If youre willing to pay a 1% premium to buy it, then some Bitshares version of coinbase might be willing to buy BTS and create bitUSD at face value, and sell it to you at a 1% markup.
Everyone in this scenario made a 1% gain, except the credit card company, who got cut out.