I played FFXI for 3 years on and off. The lawsuit is probably about the horrible way they do billing if you cancel and resubscribe.
Billing (at least for me) was always on the first of the month.
If you canceled on the 20th of January, and decide to resubscribe the 23rd of March you wouldn't actually be billed until the 1st of April at which point they charge you for a full month of March and for the month of April despite only using it for 8 days of March.
In other words they don't prorate. It's a really archaic way of handling a MMO subscription. I'm not sure if this is listed in the ToS if it's not then there might be grounds for a lawsuit. $5M is still way to excessive for what should be in small claims court for $30