If you don't know what "the queue" is, the feature probably doesn't concern you.
Also, in case this changes any one's minds, here's how either would be implemented.
For monster encounter conditions, if you set it and you hit the monster, KoLmafia clears all pending conditions and stops. On the other hand, if you manage to fulfill your conditions, KoLmafia clears your pending monster condition and says, "You didn't really need to do this anyway." The idea is there for CLI-focused players.
You can already write ASH scripts to create a virtual queue. The idea is simply to make it built-in, so that KoLmafia creates its own built-in settings-driven queue. You can access what's in each slot directly by looking up the associated property, but in_queue (or maybe queue_position) are the only built-ins that will be added. This idea is there for ASH-focused players.
To be honest, I'm biased toward monster encounter conditions since I've never felt the need to ASH script anything except as a challenge or for the now-dormant 'make holatuwol write a script' thread, but I figured I'd ask the community regarding which one would be more interesting.