Did you consider a type of continuous aggregate that works over pre-aggregated partitions for time buckets without modifications and swapping those buckets in the continuous aggregate view with a live view when data is modified? I guess it would mean that performance would sort of continually degrade as inserts/updates/deletes happened in more and more time buckets, but as soon as the aggregation event fired performance would recover. It seems like one could provide a more strongly consistent view of aggregates with this sort of approach.