what we need:
make bitXCD a smartcoin well pegged to USD with a fixed rate of 1:2.7, it can be easily exchanged with bitUSD.
1) BTS as short back asset
in this way bitXCD and bitUSD are separated, the peg rely on the price feeding, witnesses need to get BTS price in USD and then divide it by 2.7 and feed to the system, for convenient bitUSD/bitXCD exchanging, we need some big traders to provide the liquidity from both sides.
2)bitUSD as short back asset
this way bring more complex, when one need borrow bitXCD, he need to hold bitUSD first, and while borrowing bitXCD by putting bitUSD into collateral, if set collateral ratio >100%, then actually the cost for borrowing bitXCD is higher then normal smartcoin borrowing, if set collateral ratio =100%, then margin calling may easily happen if some wrong price feeding happen. some risks hide there.
this way really show more power of bitshares, but this is not the most important thing, what we need is a stable, bug-free and market tested solution.
I'll prepare to create bitXCD in 1) way if no more suggestive discussions.