>>being presented with options like negative interest rates ought to nudge people further together (I think you meant towards) current consumption
The hypothesis in the article is that the reason near-zero and even negative interest rates are seemingly required to give the same kind of nudge now is that the underlying preference for current consumption has weakened substantially. The other side of this coin being that people will now happily lend money for a much lower rate because they now value future consumption relatively more than was previously the case (the 'natural rate of interest' has gone down).
>>the underlying preference for current consumption has weakened substantially
I have a feeling this is a rabbit hole I don't want to go down :-) - but has the underlying preference for current consumption weakened substantially because of (the author's claim) that people are living longer after retirement, or is it because people feel current consumption isn't giving them their money's worth? When you hand in your dollar, you expect to receive something worth that dollar.
In other words, if people suddenly woke up tomorrow and started accepting gold as currency, will the preference for current consumption be as weak? Or will it return to the previous levels because it is easier to see if you are getting your "unit of currency"'s worth? To be clear, I don't know the answer. But if it is the latter, then people's time preferences may not have really changed.
Here's another possibility, though: what if a lot of the consumption that was stimulated since the GFC was really capital expenditure brought forward - things like households upgrading and replacing their durable goods - replacing that dodgy fridge a little earlier than was planned, that sort of thing? Eventually that well will run dry, and households might well start saving instead of buying concert tickets or whatever.