And if it is, is the problem persistent enough so that we should take radical measures to remove the lower bound? There are economists, such as Kenneth Rogoff, who think that it would be best to discontinue cash altogether, in order to liberate monetary policy from the lower bound, letting interest rates move more freely to both directions.
I think this is not the mainstream view now, however. The seriousness of the lower bound problem in the future depends partly on what happens to the average level of interest rates. This in turn depends on the return of inflation tendencies in the economy, and the equilibrium level of the real interest rate in the future.