It will be a temporary fix until Anet finds a way to cross-guest NA/EU regions server. Basically, players gets to set two home-worlds. One in EU and one in NA, then they are only allowed to play WvW in both servers.
If NA players want to play with EU friends, they get a free transfer to the EU world and then guest to the EU server the friends are playing on(If that NA player is not playing on the same EU server). If the formerly NA player wants to go back to his NA server, he can transfer back for free.
The only way for a player on a NA server to transfer to another NA server is by being on the NA server. EU players cannot transfer to another NA server that they did not set as a home world.
I would rather prefer a strict separation of EU and NA WvW:
No EU allowed in NA WvW, no NA allowed in EU WvW.
At least it is nice that the battle-balance ruining free transfers will stop
