IF a protocol could provide it, it is a nice way to rest assured that somebody isn't censoring the most subversive of the events. On nostr you can't tell. Maybe you are only getting 50% of the events, the ones the government censors allowed.

But it should be done in a soft way so the protocol doesn't break, or become inflexible. Since events can be used in many ways in many places, and there is no global store of events, it is inevitable that you will miss events in nostr. You will miss the ephemeral "king of hearts" event on the relay where people play bridge. You will miss the event that someone sends to their bunker. So clearly such a thing could not be globally applied in nostr without causing serious problems.

But maybe it could be applied in a soft way to certain kinds of events, maybe even linking back to the last 3 events meant for public consumption, instead of just the last one.

In any case, not a core/critical part of the protocol and can be added at any time we want.