You didn't understand the post explaining the new data center travel system so let me explain it in more simple terms.
1) Every single world in the game, regardless of classification, has a traveler and visitor limit. Let's assume this normal value was 3000 players for each.
2) A Congested world is going to have a reduced visitor limit (2000 players) and a greatly reduced traveler limit (1000 players).
3) When a single world on a data center is categorized as Congested, the entire data center is punished. Every single Standard world on that data center now has a greatly reduced traveler limit (1000 players). Their visitor limit stays the same at 3000 players.
4) New & Preferred Worlds bypass this data center wide nerf and will have the normal 3000 visitors allowed, and an increased traveler limit (4000-4500 players).
When a world reaches the cap on travelers or visitors, you will not be able to access that world from that transfer method. According to the JP twitter account, people spiked the login queue for travelling worse than they did previously that caused the errors and people getting stuck. That travel limit was getting hit even in other locations where the tolerance is higher. You are not guaranteed the ability to world visit or to data center travel anywhere. It is just more likely/faster to get in, if you go to New/Preferred.