I was also curious about this, and I don't think the other replies understood what was being suggested.

If I understood correctly, the aim of the engine is to lower the in-memory size of the history of game states, by only snapshotting the delta. I'm also curious what would happen if, instead, you'd just run any deterministic snapshottable physics engine, and delta compressed the history on the fly. I think this is how, for example, Braid works.

Might be that it doesn't work, that running the delta check on two big enough snapshots would be too slow, and that's what this engine fixes. But would love to hear if it was considered.