I'd make 3 zones, Zone 1 leads to > Zone 2 leads to > Zone 3.
Zone 3 would have a new HNM camp. The HNM would repop, (pulled this outta nowhere) every 10 hours. It would have a high drop rate on 1 big ticket item. The big ticket item would be on the value level of Ridill or Haidate. That drop wouldn't be rare or ex. It would be equipable by most if not all jobs, and it would be an item anyone would want. I'd definately want other treasure to drop as well, so if you didn't get the big ticket item, there's synthesis materials or some rare/ex equips.
Zone 1 & 2 I would make a town. The idea for this town is a mix of an old western ghost town & The Land of Summoned Monsters from FFIV.
http://www.rpgclassics.com/shrines/s...secrets/s5.gif
In this town, the NPC's would be dominantly monsters. The town would have an auction house, a redevous point, delivery NPC, but no Mog House. Aside from the monster NPCs there would be actual monsters you could fight, which would offer great merit party potential, also there would be either monsters or NM's that popped very frequently, or force pop NM's that would be excellent for farming gil. There'd be a large number of quests there as well as missions all with great rewards. You wouldn't be able to chocobo, but you would be able to use signal pearl in the city.
These 2 city zones would be open PvP. Unlike ballista you wouldn't get temp items or be able to /quarry. It would be a lawless zone. If you die, you would lose exp, and the person who killed you would receive 10% of the exp you lost rounded down. Rounded down so that couldn't be abused. You would be able to use a signal pearl in the city and they could assist you in PK or for great justice. It would be a virtual war zone to get to the HNM camp. You would have HNM LS's killing each other, maybe even LS pacts, or city pacts. PK LS, NA vs JP, PK LS vs Anti PKs, random acts of PK, fighting over all the good things the city & HNM zone have to offer. If a LS disrespects you or steals an HNM from you, intercept them in the city. If you don't like RMTs monopolizing the camp, you could hunt RMTs. Alot of possabilities, and it's an idea that could be grown.
Zone 3 would be safe, there'd be no PKing there, but to get to it, you crawl through a warzone. You could even make it so there's like 4 garlaige citadel type switches to open a gate to get to Zone 3, but the switches would all be spread out over Zone 2.
Think about it.