We're still close to the haircut

This is true right now but unless they are going to revise the process every time the market moves that can't be the basis for the policy.

I think "$100 worth of STEEM or 100 SBD" would be a good way to go. This gives a small discount for using SBD when the SBD peg is under stress on the low side, and costs more to use SBD when the peg is under stress on the high side (which in turn discourages burning SBD under those conditions and encourages using STEEM instead).