I think you're missing the point "Nobody can time this" and "If you haven't already, put your retirement into bonds and hold on" are completely at odds. Pulling out of equities to buy bonds is timing this.
People should have an asset allocation, and stick to it. Right now, people should be re-balancing by selling off their now overweight bond allocation to buy equities. What you're suggesting is counter-productive.
Look, until two weeks ago my 401k was tracking 14% gains. By gradually moving it over the last week and last night, I've locked in 10% gains. The alternative would have been 0% gains as of today (market is back about where it was when Trump was elected) and losses in the likely case that the market continues to slide this week.
At this point we have likely entered recession or depression territory. The rebound is unlikely to be instantaneous (unless a convenient cure is found) and when things calm down I can put my money back into the market starting from a 10% locked in gain.
People should have an asset allocation, and stick to it. Right now, people should be re-balancing by selling off their now overweight bond allocation to buy equities. What you're suggesting is counter-productive.