Comment 35 for bug 557429

Additional thoughts why updating metadata looks more limiting than beneficial to me:

Unintentional (intermittent) failures of disks won't cause conflicting changes but auto re-sync events to appear.

Segmenting an array into parts with conflicting changes requires repeated boots with separate parts attached or to manually --run separate parts of an array degraded (later hot-plugged disks).

Use-case even with reboots: Prior to doing a dist-upgrade one boots with only part of the root fs array attached, and is able to switch back and forth and rebooting the versions until to decide which way to sync.