> alternative aggregator instances (I think that's also what you're suggesting)

Nearly. I was suggesting we always do a lazy operation unless it's not possible. ```cube.data``` would then trigger the evaluation as needed.

> Actually it was just a pragmatic reason.

Glad to hear it - I agree with the approach of moving this forwards with a view to future enhancements against master. I'm glad to hear we're all of the same mind that this is a fantastic first step, but there are still further steps to take to polish.