We're back to Picketty and "r > g" here; you're not holding the pension as cash, so you're making a return, so what rate is the return at? And how does the aggregate rate of return compare to the rate of growth in the economy?

Or are people seriously proposing having 0 GDP growth and 0% interest rates and 0% expected stockmarket returns? A strange world that's almost certainly unstable.

(There is a much broader question that if you expect a dollar to buy you a loaf of bread today, is it really reasonable to expect the same dollar to buy a loaf of bread in 40 years? And what level of stasis would be required to achieve that?)