I think it would be interesting to essentially allow users to check a box to post as an 'Alter Ego' which would be a public user name with it's own post count, but no other info publicly associated with it and no public users could know it was associated with their account. On the back end, the main account and this "Alter Ego" name would be associated, however in the view of admins and/ or mods. Also, any ban, infraction etc. would apply to the parent account. Creation of this account would simply mean typing in a user name that isn't already in use on the forum.
Also, once they posted in a thread or started one and checked the box to post as their alter-ego, it would automatically associate that thread with their alter-ego and their replies would automatically come from that name.
It sounds confusing, sort of, but it could be a pretty cool feature and would probably make regular, known members way more likely to create juicy and/ or controversial content for your forum since they wouldn't be afraid to tarnish their own reputation and wouldn't have to do too much work to create and log into a separate account.