"We're currently planning on sending four waves of email invites today of equal size (but in total number of invites, larger than yesterday - yes, waves can vary in size). We're going to get them out as fast as we can, while monitoring player counts and server population. I'll update this thread when each wave is sent. You can also follow our official Twitter account for notification."
http://www.swtor.com/community/showthread.php?t=16391
But all the servers are Light and Medium... So i don't see the need in this..