I guess what I am saying is something like UHC. What I have in mind:
Idea 1:
(Will take a lot longer)
- World Bordered Map
- With that mod that allows you to make your own dungeons make some cool dungeons
- With a loot mod delete all loot and add your own in: (incorporating mods)
- Once Grace period is over map size decreases
The loot in the dungeons can either be two things. Mod items directly or crafting component like EE2's sorcerer's stone (the names something like that). If it is a crafting component it can be use to transmute raw materials into modded items (1 use)
You could also use HQM to make a kill and get loot system with mobs, or players! (Which loot can be modded items or a crafting component as mentioned earlier)
Idea 2:
Something like call of duty gun game on world bordered map where you get progressively worse modded item weapons for getting kills. First one to x kills wins