I'm sure they're going to allow it, it's just they probably have to create some sort of application process in order to give naming priority based on who made the name first, who was on the server first, who's character is actually active/inactive, etc.
Also because there will be so many people changing their names at once, it would be conceivable that names that were taken are now available and vice versa. So it's difficult to say who can use what name without some kind of system to monitor who is using what name, and who is changing their name.
In order to make it fair, they can't just simply let you delete your name and retype it. There has to be controls in place so people don't get upset, and creating a system for establishing these controls is likely the hold-up in this matter.