>> This implicitly assigns recipients a time limit, because responding too late would be considered rude. If you're receiving 500+ emails a day that expect a prompt response, you don't stand a chance.

This issue is addressed with a standard "Out of Office" response.

The difference here is that Dave is making everyone who emailed him wait until some future date to re-send any non-urgent message.

It significantly reduces the workload for Dave but increases the workload for others.

I'd be curious to hear the reaction of people who emailed him and had to wait to re-send their message.