Steem dollar collapsing in value would not represent a stability risk, it would just make steem dollar less useful.
To me this seems an inherent risk in creating a token pegged to USD. If you don't want that, peg it to something else like gold or GDP or something, or simply make a stabler coin that isn't pegged to anything but is just less volatile. For example, without thinking through the implications (and the self-reference gives me pause), I think you could have a coin that would be pagged to the 12-month trailing average value of STEEM itself. That would be far less volatile than STEEM without involving an external reference asset.
I do like the gold idea, or perhaps a basket of precious metals. It could however increase SBD holdings as it would compete with SP as a hedge against dollar inflation, plus remain liquid. Not sure if that would be a problem for Steem long term.
Gold would be best in my opinion. I guess investing in steem to try to avoid the dollar collapse would be a bad move then. lol
Investing in SBD to avoid a US dollar collapse would be a bad move. Investing in Steem (esp SP) might be just fine.
I think the idea of a third long-term-store-of-value asset that is less volatile than STEEM, but not subject to inherit the problems of USD has some merit.