I've been thinking about isolation levels... technically, it should be possible to implement Snapshot Isolation in Venice while still having A/A (i.e., multi-leader) replication. SI is not a walk in the park to implement if you have a partitioned system, but it is feasible... the A/A DCR could be viewed as the equivalent of write skew / phantom anomalies. Those are only solvable with Serializable Isolation, which is fundamentally incompatible with multi-leader.

I'm not sure I'm able to conceive what this would look like. Was the old main colo A/A via corp something that would fit this definition?

Actually, it wouldn’t be quite the real thing… I was thinking of a variant. Snapshot Isolation but without the write locks.