In large scale SMPs you typically have to limit world border size in order to force player interaction. This solution comes with the issue of limiting certain resources and potentially gatekeeping entire items(Elytra, Mace, Cactus, Cocoa beans, snow, etc.) if their respective biome or structure is not within the set border size.
There are remedies to this, such as making events for specific items, but they all require admin intervention and are very time-dependent, making players with busier IRL schedules unable to get certain resources entirely.
I propose a soft-border that debuffs the player the further away they go from spawn(Slowness, Weakness, Hunger) with further consequences the further they go (eventually tick damage that SHOULD be able to be out sustained with regeneration potions, and eventually needing regen 2, maybe regen beacons can be used to stay disable the tick damage in safer areas of the soft border)
This mod should be an addon to the traditional worldborder (it SHOULD still exist), but instead discourages players from venturing too far from spawn.