Fine-grained shared bandwidth within a ZFS pool

I've been watching an excellent ZFS presentation from Jeff Bonwick and Bill Moore and was wondering about a more fine-grained shared bandwidth within ZFS pools.

In my opinion as an enhancement each file system within a ZFS pool could have a property defining its maximum, (such as FSS scheduler) relative importance (weight) from the total pool bandwidth.

The current solution isn't flexible, we would have to create separate pools each with its own total bandwidth.
That wouldn't help the sense of virtualization.

With my proposed property we could dynamically specify to ZFS what storage policies we'd like to each file systems within a ZFS pool.