That would depend on how many banned users there were. Also, I don't think there would need to be whole versions of the site for each banned user-- there would just be dif versions computed on the fly.
I'm quite uncomfortable with the suggestion for another reason. It wouldn't work-- an active user would probably notice something was wrong in less than a day. If they were banned for excessive hostility, they'd presumably come back under another name.
My first thought was that it might be bad for the group to have people disappear for no apparent reason, but then it occurred to me that people stop posting for all sorts of reasons.
I actually think it would work pretty well. The banned user sees all of their contributions and any IP used by the banned user also sees their contributions. All other users and IPs do not see it.
I've gotten sufficient evidence from support that voiceofra has been doing retributive downvoting. I've banned them without prior notice because I'm not giving them more chances to downvote.
I'm thinking of something like not letting anyone give more than 5 downvotes/week for content which is more than a month old. The numbers and the time period are tentative-- this isn't my ideal rule. This is probably technically possible. However, my impression is that highly specific rules like that are an invitation to gaming the rules.
I would rather just make spiteful down-voting impossible (or maybe make it expensive) rather than trying to find out who's doing it. Admittedly, putting up barriers to downvoting for past comments doesn't solve the problem of people who down-vote everything, but at least people who downvote current material are easier to notice.
Any thoughts about technical solutions to excessive down-voting of past material?