I've been thinking that bitUSD, due to it's stability could spread much more easily than bitcoin.
It doesn't need a bitpay or coinbase to sell the bitUSD immediately for them to protect them from volatility risk, because there is none. So they could accept it directly and hold onto it and pay their suppliers with it, who are much more likely to accept it than bitcoin due to the lack of volatility risk. This can lead to a full bitUSD economy.
So unlike in bitcoin where merchant adoption creates downward pressure on the price, BTSX price would rise as merchant adoption increases, preserving the incentive structure.
However, I would imagine it would help if there was a payment processor to make it easy for retailors and suppliers to accept bitUSD, except this processor wouldn't need to do any selling of bitUSD to protect anyone from volatility risk.
I wonder if bitpay or coinbase would ever adapt their business to this.