The way the system is designed the SBD to USD peg will never work. What they should do is completely get rid of SBD, disable it from being created moving forward and allow the people who are still holding it to convert it to STEEM at peg value or let them keep trading it on the market, just do not create anymore SBD.
If people want a pegged asset on the STEEM blockchain wait till SMT functionality comes out and create an asset that is similar to bitUSD, even something like that is not guaranteed though...