Interesting ideas, but I don't think it would work.
Bernstein suggests increasing equity exposure as one ages. Learning to become more risk-tolerant over time.
First, semantics. Bernstein is talking about increasing volatility-tolerance over time. Not risk-tolerance (the term he uses). Volatility is objective and cannot be managed. Risk is subjective and can only be managed by knowledge. Risk-tolerance is managed by increasing one's knowledge in a particular asset or asset class. Anecdotally, after a certain (young) age, most individual's risk-tolerance (i.e. educational level about an asset class or business) is generally the same regardless of age.
Second, investing is as much an emotional endeavour as it is an arithmetical one. I don't think the emotional characteristics necessary to manage volatility can be taught. Even if it can be taught, most parents don't train their children to handle it. It's not even acknowledged by parents, let alone addressed in any systematic manner. An individual who is emotionally impacted by volatility will always be emotionally impacted by volatility. For them, the volatility tail will always wag the investment dog.
Third, even if an individual manages to get past the first two points (i.e., increasing knowledge about an asset and learning how to manage the emotions around experiencing volatility), the biggest boon for an investor is time. Starting early. Bar none. Compounding is vastly different if one recognizes the power of time earlier rather than later. Unfortunately increasing one's equity holdings at 50 years of age, to an allocation of (even) 90%, is the definition of "too little too late". And what 50 year old, who has delayed educating themselves about an asset/class, who has delayed learning how to manage the emotions around volatility, will then ramp their equity exposure to 90%? Right. Nobody.
Fourth, conventional re-balancing will virtually insure that this Black Swan individual (who has managed to address the aforementioned 3 issues) will destroy their returns. As soon as their equity exposure increases, they will take a hammer to smash it down.
Bernstein has a nice idea to try to manage the emotional fear that the vast majority of individual's have with volatility, but he's preaching to virtually nobody. I think he recognizes this, but what else can he really say? He needs to say something.
PS: The inherent lack of instruction around the emotional management of volatility is, by far, the biggest contributor to the wealth gap between the "haves" and "have nots". The "have nots" run in fear of volatility and equate it with risk, reinforcing their scarcity model of money. The "haves" run towards volatility and manage risk with knowledge, reinforcing their abundance model of money. Wealth transfer. Rinse and repeat. My opinion only.