Reclaim IPv4 addresses?
As several people have commented, we could reclaim unused addresses in various ways to stave off the crisis.
And this would achieve exactly what? Well, it would let people go on saying "We don't have to do anything quite yet" and carry on doing nothing.
And it would stave the crisis off for what, a few months maybe? Probably less time than it would take to actually do the reclaiming.
And since internet takeup is still accelerating, this would mean that when the crisis finally does hit it will be even worse.