I think in lieu of some blockchain-based (but reasonable) incentive to maintain the peg, Steemit Inc. could use their STEEM to hold the peg. I speak in ignorance as to what the burn rate would be though. It would have to cost something, and sustained over time it could cost the @steemit account more than they'd like.
But they don't seem to be doing that, so I'm willing to give this experiment a shot.
If the parameters are too far out balance then trying to force the peg by spending money can be very costly, including by potentially ending up accumulating a lot of SBD that needs to be held without being adequately compensated for the risk it could fail. It also could tie up a lot of their money indefinitely that they want to use for other development purposes.
Where direct trading can work well is once the parameters are close to a good overall balance, keeping the price stable between 99 and 101 instead of what might be natural fluctuations of 97-103 or even wider.