Wanted to bring this back up now that we have a Lodestone topic about Dawntrail congestion and travel posted.
https://na.finalfantasyxiv.com/lodes...56e40c77a5af8e
Summary for those who don't want to read the entire topic.
NA data centers: players will be restricted to their home world and worlds on the Dynamis and Materia data centers. No world visit will be available on any NA data center except Dynamis. No data center travel to Aether/Primal/Crystal except for return trips to the player's home world.
EU data centers: players will be restricted to their home world and worlds on Shadow and Materia data centers. No world visit will be available on Light or Chaos. No data center travel to Light or Chaos except for return trips to the player's home world.
JP data centers: players will have access to world visit and data center travel though there will be a limit on how many visiting players can be on a given world. If a player logs out their character on a world that reaches the visitor limit, they may not be able to log back in on that character until that world's visitor count drops lower.
Materia players will have access to world visit as usual but are still unable to visit other data centers.
Main takeaway: make certain to return any characters to their home worlds and log out on them there before servers go down for the 48 hour maintenance or you may not be able to play those characters for up to 4 weeks depending on how bad server congestion is. Restrictions will definitely be in effect until 7.01's release (July 16th). SE may choose to extend the restriction period to 7.05's release (July 30th) if congestion continues to be severe.
If you wish to play with friends that have different home worlds for their characters, you will need to meet on either the Materia or Dynamis data centers.