The idea here is that although some resources may only be consumed in a revocable manner (e.g. oversubscribed resources, resources from "spot instances", etc), other resources may be consumed in a non-revocable manner (e.g. dedicated instance, on-premise machine).
However, a scheduler may wish to consume these non-revocable resources in a revocable manner. For example, if the scheduler has quota for non-revocable resources it may want not want to use its quota for a particular task and may wish to launch it in a revocable manner out of its fair share. See:
In order to support this, we should adjust the meaning of revocable and non-revocable resources in order to allow schedulers to decide how to consume them. The scheduler could choose to consume non-revocable resources in a revocable manner in order to use its fair share of revocable resources rather than its quota.