blkdev should implement power(9e)
blkdev should implement a working power(9e) interface. This means that it also needs to provide an optional entry point for its consumers (the underlying block device drivers) to implement. This way it can reasonably power down storage devices not in use as part of the system power management policy.
This is low priority, because current blkdev providers are implemented in terms of solid state storage, and consume very little power when not in use.
Note also that its reasonable that the provider can handle its own power management needs without help from the framework.