Stardock plans to implement personal banlists. I'm not sure if that's a good idea but at least the potential for grieving and abuse is minor. Right now the biggest problem for many players is to get into a game at all. People are getting kicked for all kinds of unjustified reasons (like a ping > 100) and you are not helping the online community in any way, quite the opposite.

BTW, it's easy enough to change a username and real griefers/rage quitters can just change their username and escape 'your justice'. It will most likely only hurt newbies who are trying to take their first steps online and Sedna/QoT players who ran out of mana and failed to save some idiot charging into enemy territory. Or a bunch of people might just ban a good player because he's 'SO ÜBER, HE HAS TO BE HAXXING!!1!, LOL'.

I hope you rethink your whole idea considering how much harm can be done compared to how little your banlist might help the community. The vast majority of the community and Stardock employees told you it was a bad idea. That alone should be enough reason to shelve the project.