The only thing it means is that it won't be region locked like in WoW, SWTOR or Rift. An NA WoW account cannot be used on EU servers. Same for SWTOR etc. The list of server displayed will only be the ones of the region of your account.
For XIV, the way I read it is
"You can pick any server you want, regardless of its geographical situation and the region of your SQEX Account".
So as a French player, using an EU account, I could play on an EU, NA or JP server. World transfer between these as well. But playing on NA or JP will mean higher latency for me. Others MMO don't allow that. You are only free to move from servers to servers within your region. (Which often have a single language tied to them for EU.)
Edit : Nvm I did reread your post, we say the same
By 50~70ms top from EU to JP. That's not a lot and would still remain 200ms+ for EU. If you want to reduce that by "a lot", be the next Nobel prize in physics and find a new way for data to transit faster across the globe.Cross connecting servers and keeping them in sync is not hard, and it will not cause more lag, a standard internet connection fluctuates a lot because of potential problems a long the path, however if SE gets control of how the traffic moves it can reduce lag a lot