If we pass the 10% haircut limit, let's say even to 20% - that is a risk for SBD holders. In this (hypothetical) scenario - SBD could drop down to $0.5 USD.
In that case (1 SBD = 0.5 USD), should SBD holders not be able to convert to one USD equivalent of STEEM?
No. If we pass 10% debt level, then SBD conversions would pay out less than a dollar worth of STEEM. At a 20% debt level, it would pay out 50 cents on the dollar.