This is more of a website question / request, but I'm not sure what folder to post something like that in, and this is about upgrading to platinum on the website.
When reactivating an account, eventually a screen pops up to show what characters you had before and decide which of them to devote character slots to.
I'm sure some people coming back to plat did what I did: first reactivate with the basic subscription to try out the game for a bit, and then sign up for plat again.
I'm not sure if this is even feasible, but it would be awesome if that character screen could come back up when upgrading to platinum, so you can bring your old plat characters back. I've emailed support to work on this manually, but I thought it might be a good suggestion and incentive to bring people back.
~Rythanack