This will lead to a jump in the price of SBD, while the price of STEEM may not decrease, as the conversion will go directly from STEEM to SBD.

Good point. I already mentioned the uncertainty about the price of SBDs, but I should have mentioned the selling pressure on STEEM, too. I just added that to the main post.

In the long run, this will lead to a glut of SBD in the market and a drop in its price.

I also suspect that in the long run, this would drive the price of SBD back towards the peg, but I think it all depends on whether investors and authors sell or save the SBD that they receive in interest payouts and author rewards.