It's not much of a singularity if there aren't real economic gains. I see no reason that prices of tdoay's typical consumption goods should go up. In fact, most of them should drop precipitously. Pricing of positional goods will skyrocket and become unaffordable to those who didn't create enough value or capture enough rents during the transition. It's hard to say what will become of economics in a time of no scarcity, though. I think most "needs" will become essentially free and the economy will consist primarily of positional goods.
One could argue on this definition that we are already pretty close to such an outcome, at least in the rich world.
Taleeb's advice is extremely faulty, at least for long run investing. The black swan event that makes a more fully diversified debt/equity portfolio fail disastrously in the long term (20+ years) has a fairly high likelihood of taking out a short-term US treasury portfolio as well.
More importantly, while it may fare slightly better on average in the event of a complete meltdown in riskier financial markets -- short of that, it will almost always do quite a bit worse. If the chances of that meltdown are, say, 10%, we have to weigh insurance value in that scenario (which as Eliezer mentions is hardly perfect) against being many times as well off the other 90% of the time.