I've long ago realized that archival needs to be a separate task left to archivists and archive systems. If you take it into account when designing a live system it's liable to seriously compromise your system design.
Say you're making a chat app - you wouldn't incorporate a delete feature, and you might be tempted to use some kind of blockchain to prove all messages were delivered without gaps. But if you ignore archival needs you design something similar to IRC which is much simpler.
