[PhantomGremlin]

I don't think this will do what you want. One limitation is:

   Currently, device removal only works if all top
   level vdevs are plain disks / files. At the very
   least, we want to make device removal interact
   intelligently with mirrored disks.

I think that statement means that this feature will not work with mirrored or RaidZ* configurations.

[X-Istence]

It's a start, from here on out this can only mature and other use cases can start being considered.

[craigyk]

yup, hopefully removal of any top-level vdev and rebalancing data in a pool.