They already have a solution, but they're just sitting on it. Bicolor Gemstones should be given by FATEs in EVERY zone of the game, with maybe random bonuses that change every hour across all regions, maybe two at any given time. They should also have more untradable items that you can only get with said gemstones.

Not saying that that's the only thing they need to improve the world zones, but the gemstones are already in the game, we only need more incentives to get them and have them implemented across all regions.