Thanks for replying on this important issue.
Yes at the moment most of your customers will use BTC to buy BitUSD. There is a psychological issue here because your customers will want to know that they are getting a fair amount of BitUSD for their BTC, in other words the SAME amount of BitUSD as real USD if they were on a US exchange.
By swapping the pair around you are making it harder for customers to understand and be convinced that they are getting that deal - they want to see a price around 235 not 0.004. Maybe that's why the BitUSD:BTC volume on yunbi is near-zero.
I dont understand your point about arbitrage - the internal exchange markets can be swapped with the button at the top of the gui anyway.