### What would you like to be added?

We're using `maxUnavailable` in a stateful set with an `OrderedReady` policy. A few issues/enhancements we would like:
- It's terminating the pods in parallel but the whole initialization process (`ContainerCreating`/`Init`/`PodInitializing`) is still happening one by one, can that be done in parallel too?
- When scaling down (and up) `maxUnavailable` is completely ignored, the pods are still terminated (and initialized) one by one, can that happen on parallel too?

### Why is this needed?

We have a stateful set with 32 replicas, deploying and scaling takes a long time, by using `maxUnavailable` we have been able to improve performance by a lot (from over 30 minutes to under 5 minutes), we believe that if the initialization will also be made in parallel we could bring it down to under 1 minute.
As for scaling down, because it's currently one by one, it still takes us ~30 minutes, and we would like to make it as fast as deploying.
Make `maxUnavailable` more useful for StatefulSets with `OrderedReady` Pod management
This is a GitHub Issue
repo:kubernetes
owner:kubernetes
Title : Make `maxUnavailable` more useful for StatefulSets with `OrderedReady` Pod management
Issue date:

--- start body ---
### What would you like to be added?

We're using `maxUnavailable` in a stateful set with an `OrderedReady` policy. A few issues/enhancements we would like:
- It's terminating the pods in parallel but the whole initialization process (`ContainerCreating`/`Init`/`PodInitializing`) is still happening one by one, can that be done in parallel too?
- When scaling down (and up) `maxUnavailable` is completely ignored, the pods are still terminated (and initialized) one by one, can that happen on parallel too?

### Why is this needed?

We have a stateful set with 32 replicas, deploying and scaling takes a long time, by using `maxUnavailable` we have been able to improve performance by a lot (from over 30 minutes to under 5 minutes), we believe that if the initialization will also be made in parallel we could bring it down to under 1 minute.
As for scaling down, because it's currently one by one, it still takes us ~30 minutes, and we would like to make it as fast as deploying.
--- end body ---
