The author wants zfs to support growing and shrinking pools in a specific way that it doesn't support.

However it's clear from the docs that you can grow zfs pools by adding new vdevs. Shrinking a pool is not possible.

In practice I haven't seen the inability to shrink pools as an issue. I simply do not create pools from entire disks and use partitions instead. For example each drive is split into 5 partitions. And if I need to grow a pool I add another partition across all my disks to the pool as a new vdev.

This also allows me to have multiple pools on each system that have different Raid-z levels based on different app reqs.