I don't think thor is required as the master ban list can just be a text file, as BZFlag's is, http://www.bzflag.org/master-bans.txt, so you just need to make a server load the list when it starts and when anyone joins that matches entry's in the list are kicked

Clearly this topic has died recently but the idea of a global ban list or "Master Ban List" is a great idea.

I play a game called BZFlag and they have a master ban list
http://wiki.bzflag.org/Master_Ban
and the list:
http://bzflag.org/master-bans.txt

Take a look
It works really well