Well, right now SBD comes from reward payouts, which is what automatically ramps up with the STEEM price, so if you got rid of STEEM reward payouts you could, and indeed would have to, completely change the mechanism surrounding how SBD gets created.
However, you can't in general place arbitrary controls over the supply of any stable coin, or it won't remain stable. You have to choose between stable price and unstable supply or stable supply and unstable price (or perhaps some point in the middle with nothing being actually stable, but just volatility-dampened).
The DAI protocol does the supply control required to keep it stable. Evidently, it has managed to hold close to $1.00 even through very volatile phases.
All STEEM has to do is manage its debt to DAI. Which, yes, will require a paradigm shift, not ramping up DAI purchasing when the price pumps temporarily, etc. All of this is just throwaway thinking-out-loud, of course, and I'm well aware it's not going to work for multiple reasons with Steem in its current state.
It keeps the price stable, not the supply. The supply can ramp up very rapidly, even more rapidly than SBD.
Another semantic misunderstanding, I meant supply control = controlling supply to keep the price stable. I didn't mean supply stability, obviously.
I guess I just don't understand what you propose to use DAI for or how it would be used, but that's okay, we both know it isn't going to happen realistically.
I was just thinking out loud, since the argument is that there's a need for stablecoins on Steem, and other dApps that need stablecoins are starting to integrate DAI. Obviously, it's never going to fit the current Steem model, so let's move on.