The endgame isn't the Japanese population reaching zero. Eventually, real estate prices will go down and, with increasing automation, having many children will again become affordable. There will be pain on the way there, as the infrastructure will degrade and many elder people will lack caretakers. But I believe the market will slowly adapt to the situation and create incentives for a new population equilibrium.
Birth rates don't appear to be reacting to that sort of economic incentive so far, as tried in other countries. Possibly it's just not enough or being done wrong, but that's not something you want to bet your country on.
I agree you won't bet your country on this hypothesis. At the same time, I'd expect the reaction to take a while, perhaps over a couple of generations. We need a generation where having kids is cool again, but the incentives need to be well in place for that.
