SBD technically kind of already a SMT. Stable tokens will definitely pop up as SMTs but what makes SBD different is that it's on-chain and non-custodial. We can't make SMT that works like DAI on Steem because Steem doesn't support custom smart contract on the base layer, we can only make custodial stablecoin like Tether with SMT specification as written on the white paper let alone the v1 coming next fork which doesn't have the full specification yet. However, we can push a change to make SBD work like DAI (or other on-chain non-custodial stable tokens) if we want to keep it around at all.