The downside with waiting to retire, for any reason, is that you've worked longer than you presumably wanted to. The last recession in the US ended 10 years ago. That's a long time to wait.
The other thing is, if you're going with something like the 4% rule, then that is already going to survive all but the worst times to retire in history. There's also layers and layers of other safety margins - even during a recession, you can probably get a job. Maybe not as good of a job as you had pre-recession, but when you've got mustache-level spending, even minimum wage goes a pretty long way. Then eventually you get to where you can collect social security. And damn near everyone has some fat they can trim from the budget if needed.
Suppose you could go with something like "retire at 4% if during a recession, 3% if not", but that's not for me personally. Once I hit 4% I'm pulling the plug. Maybe 5% - check out the broke/dead charts - we have an awful lot of angst over an overall unlikely outcome of "broke".