I'm relatively new here and I've come to love this server a lot.
I'm pretty dumb so my suggestion might be easier said than done.
The idea is a Horde Event ( maybe purchasable through store or random occurrence like Garrison )
where an ungodly amount of zombies spawn THROUGHOUT one quadrant OR they can spawn surrounding a "ruined" generated base.
I'm unsure how feasible this is considering how much strain it'd cause the server, but it'd be a fun group event for everyone!
Unsure if any prize is needed however some loot hiding in the center of the horde could incentivize people to join.
Thanks for listening!