Im no longer a staff member but its really easy to come years later with something a lot of people may have forgotten.
If he is unbanned, it should be done only after the person who punished him explains the situation if he/she remembers it.
If it was so unfair, why not making millions of unban requests at that time? If someone made the decision it almost certainly has a reason, we cant doubt what old staff members did because someone just says that years later.
Lets wait for ZengZ to come back in five years saying that my permaban to him was unfair. If noone remembers or wants to remember, yes it was unfair, if someone remembers, well then we will all know that he destroyed the entire AC spawn and made many staff members to spend their time fixing it.
Or lets wait for CapitanParaguas to come 5 years later saying that my permaban was unfair and that he spent his time and regrets it. He had a permaban because of all the damage he caused to Network and his many other offenses. But yeah, he could come back saying he is sorry and that we should forgive him. If someone made the decision of being permanent is for a reason. If we wont respect this reason, then all this system has no sense at all. He had his time to ask for an unban.
EDIT: of course you can pay to get unbanned as many people did.