That really only leaves OSRS GP Mediterranean/Southern Europe, so it would be logical for the new continent to resemble Italy/Spain/Greece. Iron age concepts could be integrated in this scenario, I think. Imagine two cities that have significant characteristics that resemble Rome or Carthage.
Although they're not in conflict, the two were at times at one time. The current standoff is tense. You will be attacked by hardened foes when your character attempts to travel on the road between them. There are two options to choose from: You can pick one of the cities "good" or "bad", and your character could choose to fight for either or both be on equal footing.
The region north of these cities is colder, wetter and more mountainous. These people would appear a lot like Celts, and are considered savages by the southerners. They look somewhat like Fremenniks, however they are hunter/gatherers and live within smaller communities. They also have a conflict with city to the south, which are trying to expand their territory. This could be a perfect place for a dungeon to be raided should Jagex desires.
I'm not sure the reason this is being forced on us, according to a poll, solo bosses got twice as much support. Jagex keeps polling and players keep saying that they don't want. This is going to make it seem like an artisanal situation. OSRS needs a complicated solo boss that is similar to the QBD 2012. Similar to the QBD I say this because it was originally an old combat system that was quite basic but had complex mechanics that were not in the current. While I'm not convinced that the mechanics are identical, the dragon kiteshield might be a good drop.
There's no reason for old school rs gold me to try again. I don't think there is something that would inspire me to desire to see the game repeated. I don't find the game interesting enough to make me want to get into it. Heck I've never been a fan in gaming, therefore I've not bought Fallout 4.