Moving Git past SHA-1

Hm. Given that the transitions will always happen at a parent/child commit boundary, you're probably right: the delta compression heuristics are partially commit- and partially file-based, so even the smallest window will find and scrunch them into nothing.

OK, all my objections to this scheme are gone then: except for a slightly increased diff cost across the boundary (to, uh, what non-git users pay all the time) it is costless. :)