As much as I've always wanted this, I'm pretty sure this is a thing in the majority of MMOs because of technical limitations. Like, you are picking a server in EU because you want to be closer in proximity to it and routed to it more efficiently for better ping. The same thing with vice versa, depending on where you live. In order for NA and EU players to be able to play together, they'd need to be connecting to the exact same servers. This isn't possible to do without the majority of players noticing a large increase in server latency. Additionally, the separation also exists because they try to separate the communities based off of language. While it may not bother you or myself, a lot of people simply don't want to read people constantly talking in different languages that they don't know-- at least, they don't want to see it constantly. Most people want the community to feel as relatable as possible. Imagine if for example we were all able to play together, and use the same LFG. Can you imagine first of all how crowded it would be and how often it would be where people would get frustrated from not speaking the same language and stuff like that? Last but not least, they profit from gem sales on server transfers-- it would be a complete loss for them to remove the regional wall in all honesty. There would be no chance for any pros to outweigh the cons. Hopefully the points I've brought up will give you a bit of perspective. Again, I really wish I could play with people on NA and EU at the same time... but I understand why things are the way that they are. However I will also say that your suggestion of at the very least allowing you to guest to a server across regions would be pretty nice, just a server transfer with a time limit essentially.