I have a concern with the collateral being enough to cover the debt by the future date... there is a responsibility on the bond holders to keep an eye on the price changes of BTSX/BitUSD to make sure their bond has enough collateral value to pay the debt at the future date. In fact, in theory if the collateral isn't large enough to cover a drop in the price of BTSX from when the bond was purchased until when it pays the debt, then the effective interest rate can decrease and even become negative.
The part where I see the biggest challenge is such collateralization working on a blockchain. I can not figure out a way (neither have I read somebody suggesting working solution) where both conditions are met -repayment of the bond (debt is) guaranteed and at the same time incentive for the issuer of such bond is still present. In other words if the whole amount received through the bond sell is kept as collateral + additional collateral for the interest is needed, where is the incentive for the issuer? Anything less than that collateral leaves the bond buyer exposed to the risk of not receiving his money back.
[edit] It will take a truly independent bond market, where special market participants, will act as bond issuer and will collateralize a series of bonds (with deferent expiration dates), for this to truly work.
A bond that pays 1000 bitUSD on a particular date in the future (face value is $1000) must initially be backed by 2x that value in BTSX by the issuer. The issuer is responsible to maintain the margin just like a bitUSD short; if the collateral value drops to 1.5x the issuer is also subject to a margin call and bitUSD is bought off the market to cover and bitUSD is deposited into the collateral account. If the issuer doesn't fund the bond collateral with bitUSD by the maturity date (payout date) they are also subject to a margin call on that date.
I think the chance that the margin call can't find a bitUSD seller at the price needed is VERY small. In that event, the bond holder gets the BTSX shares instead. (just like if a company can't pay a bond, then the bond holders can take the company)
If the issuer sells this bond for $950. They can then buy more BTSX to get more exposure to the upside of BTSX. Or do something else with the money raised while maintaining their exposure to BTSX in their locked up collateral.