I'm the one working on this right now and this is exactly what I'm doing. However, old document bodies are not the only way to store history. Documents have a revision history, possibly 'stemmed' to a maximum height, which is an array that traces a path from a certain depth back toward the root. All the leafs are conflicts. This is the algorithm davisp is talking about.

While I'm not going to leave the document bodies of superseded revisions accessible (by overwriting them in IndexedDB), I still need to store these history paths so that merging a new revision (either via interactive edit or replication) can properly generate a conflict when applicable.