We sortof kindof operate with a system like this, except the content and context of an offense can vary greatly, meaning we as staff need to judge what happened and make a decision based off of it. This often translates to roughly 2-4 "strikes" (though I don't think that's an accurate term for VC). Sometimes less, sometimes more. It all depends on the circumstances and severity.
For example, if someone with no prior offences griefs a house, we would punish them based on the extent of the grief, how malicious it was, their response, and sometimes the input of the victim. We generally give at least one more chance. If that person griefs again, in most cases I would recommend they be banned. But perhaps the 2nd grief is minor and they are apologetic and willing to fix the grief immediately - they might slide by without a ban or with a lesser punishment. Alternately, they might break a totally different rule, in which case they may or may not be offered a second chance for THAT offence as well (this is sometimes a reason for people having more than 2 or 3 offences without being banned).
And of course, we judge people based on how they act, whether we think they have the capacity to change or repeat the offense, and their prior offences. Ban/punishment appeals are based on all of these factors as well as what they actually write in the appeal.
So why do some people get more unbans? Usually because the staff in question have made judgements that the person has a good chance of being a good player from now on. We make mistakes sometimes, but we also want to create a fun environment, and we generally want to help people become better people. Sometimes letting them come back to prove they have changed their ways is worthwhile, and indeed it has spawned many good players (and some staff too!) that would have never had the opportunity on a ban-first-ask-questions-never kind of server (as most are on Minecraft).
Thanks for sharing your ideas (though we won't be adopting this system on VC).
Sidenote: Though somewhat rare, in the past I have supported immediate permanent bans regardless of prior offences for real harassment and bullying. I think your 1/4 or 1/2 strike for those are too soft. Actually, I think all around you are softer than VC.
