It will be us BTS users who decide what spreads shapeshift will charge for their conversions. The higher volume we trade on the exchanges and on our internal DEX, the lower the spreads will be, and similarly the lower spreads shapeshift will charge because their spreads will be exchange spreads + small commission. If we want them to integrate bitBTC then we have to make sure that the BTC/bitBTC spread becomes very small, by trading it as much as we trade bitUSD. Right now the spread is more than 10% on the DEX so I don't think it's viable yet.