If you think it is rough with 2 to 5 characters, then imagine having 20 max rank characters like myself! It is absolute torture completing the missions for "Special" prizes with the current setup. The easiest way is to make it a Veteran Reward not based on time, but based on number of characters. The fact that the 1,000 day Vet reward was basically given away needs to be blocked from enabling somebody to claim a relief reward like this.
What's in it for Cryptic if they make it an account unlock?
If they keep it per character then there is more incentive for people to buy keys, get lobi, and convert to pearls. Cryptic will only make something easier for players if there is something in it for them, in this case they would lose out if they made them account unlocks.
Man is a gaming animal. He must always be trying to get the better in something or other.