Crazy thought: something like BorgBackup. If only 20% of the content gets changed, the rolling hash that Borg does to chunk files could identify the 80% common

Crazy thought: something like BorgBackup. If only 20% of the content gets changed, the rolling hash that Borg does to chunk files could identify the 80% common parts and then with its deduplication it would store just a single compressed copy of those chunks. And as a bonus, it's designed for handling historical data.