I am aware that there was some talk about sigbans but I would also like to propose a merit ban.
Certain users that have an ok/good reputation and previously had 1 old plagiarized post (an interesting one that might be considered merit bait) could get a temp or permanent merit ban (maybe along with other forms of bans).
Not sure how much code would have to be rewritten but as these should and are handled on a case-by-case manner might be a useful tool when needed.
I'd be in favor of a ban that would basically turn high-rank offenders into newbies (take away merits, signature, etc) but let them keep their account and continue on the forum. Most would disappear anyway, since they're here for money only. This has been proposed is some shape or form multiple times but I wouldn't hold my breath. For now the only path is to get theymos' personal attention with a "good for the forum" appeal and get the permaban downgraded to temp+sig ban.
Update May 15: now global moderators have been given the option to do signature bans so appeals should move faster and new plagiarism cases may get temp+sig ban at their discretion without the need of appeal.