SBD has not "failed to deliver", it was given two jobs to do, and it is doing one job better than the other. I will soon write on this and don't wish to write the post in this comment. SBD is part of the stability-mechanism of the whole Steem economy - that is what it is doing now. The idea that it is also a stable coin relies on human intervention, such as assigning it an interest rate. Thing is, trying to prop it back up to $1 will conflict with its algorithmic task as a debt to steem. All issues that require simulations, not just ideas.