I think its completely fine to start off with region restricted DC travel. It gives the developers an opportunity to both test and observe the systems, as well as see the impacts it has on market economy and player interactions.
When world visit was introduced there was significant worries that that would impact the in game economy too much, but that turned out to be fine.
On different data centers and servers there is different etiquette for how one behaves and what topics are acceptable (for example), this is a clear concern for how it will affect player interactions and a healthy environment.

When DC travel was first mentioned, it was said that they would most likely be opening up in-region first.
If they choose to implement worldwide DC travel and it turns out to be a mostly negative affair, it'll look really dumb if they have to turn that off again.