It means that one of the 2 servers (at least) is scheduled for a server connection, they will probably announce it on Monday/Tuesday (blizzard US time)
If you cant transfer anywhere its def Aman’Thul thats locked.
EDIT, I did a little digging, these are the realms I could find that are so far blocked off, its 100% related to the server connections and it seems like blizzard has thus far only blocked half of them as no other OCE realms are blocked off yet.
- Black Dragonflight/Gul’dan/Skullcrusher
- Hydraxis/Terenas
- Darrowmere/Windrunner
- Aman’Thul
- Ghostlands/Kael’thas
- Exodar/Medivh
Edit2: seems like the destination is Dath’remar/Khaz’gorath, you can transfer after the connection is made on the 17th…