I think the collateral and a 10% APR should be enough to hold the peg, the reason you see a price below 1 dollar now is because of a downtrend that keeps the exchanges price below the 7 day average shown on steemd, if or when price of steem stabilizes or increaes then you will see SBD at 1 dollar or above... I personally dont think we should assume that the SBD will be 1 exact dollar always, it will most likely vary from 0.80 to 1.20...

SBD has been alive for exactly 1 month today.. it has been below 1 dollar and it has been well above it too, so in my opinion is too soon to be thinking of changing the interest rate.