The entire region of Runescape currently represent

You take out the contents of  OSRS gold all four. The original Port Roberts idea is better. Port Roberts could be the main tie between Asgarnia/Kandarin/Misthalin and the new continent, and resemble those areas more than the rest of the continent.

I don't like how there are gnomes in this game which is a bit odd since they're not sailors, but I like the idea. The trade between the continent of Africa as well as other parts of the globe is controlled by the customs authorities that is taxed heavily and makes it difficult, etc. People are using illegal smugglers, pirates and other criminals to conduct their business. This is because they are not happy with the customs authority. The conflict between these two forces can be explored through quests and you can decide to support either of them. Colonial Boston is the closest thing I've come up with to a real-life approximation.

The entire region of Runescape currently represent some part of medieval Europe or the region to the east. For example, Fremmeniks-Scandanavia, Karamja-Sub-Saharan Africa, Asgarnia/Misthalin/Kandarin-England, Morytania-Eastern Europe, Al Kharid-Arabia.

That really only leaves Mediterranean/Southern Europe, so it would be logical for the new continent to resemble Italy/Spain/Greece. This could include the concept of iron age. Two major cities could be built that look like Rome or Carthage.

The two are not in conflict, but they were in the past and are currently in the middle of a standoff that is tense. The route between them is heavily guarded and you will be attacked by fierce enemies if you attempt to travel on it. You can decide to choose one or two cities and then you can have quests in which your character fights against the city that is evil. Or  buy RS gold you could have them all on equal level.