RE: Steem Dollars have Limits
If the USD hyperinflates (which I disagree with you regarding it being more likely than the other type of black swan), then the witnesses could just transition to tracking the price of some other asset with reasonably stable value.
We should have in parallel more that one "stable" assets. Why waiting the $ to collapse and then making the switch? (it will be too late if it happens too fast) We should give the option to the steemit users to get paid on any currency they want! Steem Dollar, Steem Gold, Steem Bitcoin, Steem Silver, Steem Yuan etc.. So in case one of the"stable" steem currency collapses only a part of users would be affected and not all the project! Right now we are vulnerable to a one point of failure and that is the US dollar value (how ironic would it be the steemit project to die because of a FIAT currency fail!)
At some point it might sense to switch to Bitcoin. Bitcoin would need to be much more stable and much more widely accepted before this is feasible but I don't see hyper inflation or deletion anytime soon.
There are trade-offs either way. US dollars will likely bring in more users outside of the crypto world, but it has a real threat of hyperinflation, given enough time. Too many markets, as you suggested, would cause confusion and create illiquidity in markets. Gold may provide a nice balance. Its likely to never hyper-inflate and its a single market that most users on earth can relate to, although with a bit of perceived volatility.
People perceive volatility in gold because they are measuring its value against fiat currencies whose prices float against each other. "Two sides to every coin", so to speak... which asset is volatile? the metal or the paper currency? It's a reflection on the instability of the fiat money system that exchange rates on currencies fluctuate so much against each other and nations engage in currency wars to game the system.