I don't think theres any type of fully trustless BTC gateway (sidechain) but some proposed are very secure and would be good enough to use as BTC collateral for smartcoins.
This would be huge! And a real win for bitshares / marketing opportunity.
Just think any bitcoin holder in the world could get a USD loan against their BTC.
For those of you worried that this would damage the value of BTS I disagree because all fees will still ultimately be paid in BTS even when paying or collateralising in SIDE.BTC
I see the system inconsistent. SmartCoins are self-assured, but if tomorrow morning the Gateway has disappeared, or has been banned or hacked, who guarantees the collateral?
If I am BitUSD holder and there is a black swan event I know I will receive at least the collateral. What will I receive if the Gateway disappears? BTS? From where?
If it is not possible to find clear answers to these questions that would imply that BitUSD would become a weak asset totally dependent on the Gateway's survival. Crazy.