What would you like to be added:

The ability for an admission check to influence when preemptions happen (anytime vs after the check has passed).

Why is this needed:

It might be useful if an admission check could take a long time to be satisfied, so that preempting early is not very useful.
However, it's unclear whether the usefulness of this feature outweights the complexity of moving the preemption logic outside of the admission loop. Especially as we start thinking of #62 and #998.

Completion requirements:

This enhancement requires the following artifacts:

• Design doc
• API change
• Docs update

The artifacts should be linked in subsequent comments.