I'm not sure if it SBD and Steem will reach parity again. The idea is that one SBD should be one USD. I don't see SBD increasing in value to reach Steem since it's wise to buy Steem with it to power up or trade it for some Ether or Bitcoin on Binance. SBD only has demand because people prefer to have 50-50 post payouts because they believe the SBD amount they get to be worth more than the Steem, but they often convert it into Steem increasing the ratio.