People with level 1 character names.

[Leash]

I know League of Legends does this. If you don’t log into the account for over a year it sends out a warning that if you don’t log in within 30 days or so, it will release your account name and make it available to someone else to use. Your physical account will still be there, you will just need to make a new username if someone else hasn’t taken your original username. I remember getting one of these a long time ago (before LoL got popular).

They could implement something like this with logging into Mog Station and verifying that you want to still keep this character's name, without the need to pay for a subscription to log in.

[Naraku_Diabolos]

I have 4 characters total, and one of them is a Lv1 character with a unique name. I'll be using him once my girlfriend comes to the U.S. on the fiancée visa so we can play together. She lives in Japan right now.