The only changes I'd really like to see to horde nights are more variety and variability. Variety in horde sizes, intensity, and trigger event would also be nice. Sure, base it on game stage so it gets harder as you go, but...
How about a POI that is a horde spawner? Zombies keep piling out of it at X per minute once you get near it and won't stop until Y zombies have spawned and/or you finish the "POI proximity quest" that started the spawning in the first place.
A small horde that appears shortly after the first time each type of crafting station is built and placed in the world (or once per day per crafting station type placed).
A horde that appears shortly after you've reached certain milestones in the skill trees, such as reaching level 10 in a stat or the highest value for any skill.
Have a chance for a few zombies to appear as you butcher an animal.
Setting off explosives (and other loud events) should trigger mini hordes. This used to be a thing but now it seems very rare at best. Using a chainsaw to cut down trees used to almost guarantee a screamer showing up, for instance.
Zombies that are like sleeping screamers. They will sit there and do nothing but face a certain direction out in the open (not in a POI). If you cross their field of vision they will trigger a mini horde. If you kill them from behind and quickly, no horde spawn.
I could go on...