This is just my guess, they may be giving everyone another free month on top of the included free month that comes with the game.
If that is the case, it's possibly a gesture of goodwill to everyone for putting up with the first two weeks where no one could log in unless they left their PC on for a day or more.
The other possibility is that they will start charging the monthly sub once the Myrland main server is upgraded sufficiently to support 10k+ players and the remaining two alt instances can be removed. They have already removed two of the four instances with the latest patch.
Again, these are just my speculations only.