I think this is an interesting idea for trading assets like indices and stocks.
In the future when we have a strong bitUSD, bitEUR, bitCNY, I'd like to see the trading assets all denominated in those currencies, with margin accounts that are also denominated in the same currencies. I think this would be more attractive and familiar to traders than trading bitAssets denominated in BTS.
In that context, the settlements (which could be quarterly expiries for example) on these trading contracts could coincide with points in time where simple centralised feeds are possible. That could remove the need to rely on human-routed feeds. Continuous free-market trading could however take place right up to expiry, as there is no forced settlement that could harm any party till expiry. (Margin calls get covered at market, and its OK if that's not a "fair" price).
With bitAsset currencies like bitUSD itself, its maybe possible but a bit trickier because they need to be settled in BTS, which exacerbates the risk of BTS manipulation if settlement occurs in confined windows. With a more liquid form of collateral (such as a collateral token directly convertible to BTC) this would be less of an issue.