It is not the job of witnesses to maintain the SBD peg.
It is part of the job of witnesses to publish the actual STEEM exchange rate (aka price feed). It is also part of their job to publish an interest rate for SBD as they see fit.
IMO the current disparity of SBD/USD is due to two main reasons:
- the downtrend of the STEEM price means that SBD->STEEM conversions take place at an exchange rate that is too high, due to the 7 day median
- the market is not sufficiently informed about SBD, in particular I think that many market participants know neither about the pegging mechanism nor about the interest rate
Both points are out of scope for witnesses.
many people get confused about the main purpose of price feed mechanism.
Let's make it clear:
The present of price feed is NOT to mimic the STEEM/USD price at external market,
but to give a suitable STEEM/USD rate that could help maintaining the SBD-USD 1:1 peg:
This sentence is not mine, but an excerpt from the White Paper. (page 14).
I think you are interpreting too much into this.
It is impossible "to maintain a stable one-to-one conversion" in the strict sense only by adjusting the price feed and interest rate.
For example, if one reason for the current difference is the 7 day conversion delay in combination with the steem price downtrend, we'd have to adjust the price toward the expected median in 7 days. That median however is computed from the price feed - meaning you have created a price feedback loop. Which is a very bad idea, since loops have to potential to resonate catastrophically and are not easy to control.
The reasonable thing to do is publish a feed price that matches the market rate. The result will be a long-term stable SBD price that oscillates around USD parity.