Additional Use Case

Your main use-case is geared at swapping alternate blocks, but there are use cases for just being able to "un-publish" a block on a schedule.

Example: For reasons I won't go into, I need to embed Google Analytics tracking code up to a certain date, but not beyond. Traffic is high enough that I would prefer to be able to trigger the tracking to stop at midnight in the relevant time zone, to ensure clean reports.

You could create a rendered block that's un-published on a schedule by using nodeblock & scheduler together; however, that's a less than ideal solution for an un-rendered block, or for a block that's not exposed to scheduler.

Classifying as a feature request because it might mean changing some thinking around design. Do with as you will.