OK, hear me out.
We have the per-user upload limit for a reason, right? It's to limit the damage done by one malicious individual who creates an account to start spamming IRL gore or what have you. The upload limit is a sign of trust: as more of your posts get approved, you gain the right to upload more at once. Conversely, the more of your posts get deleted, the more trust you lose, and if you post nothing but garbage, eventually the privilege is taken away altogether.
Right now the only tool the site has for curtailing other forms of vandalism is a crude global count. I mention tag edits because they've been on my mind after looking at the (former) results of no_pants no_underwear no_bottoms and groaning, but that's hardly the only large-scale vandalism possible. Hands up who remembers that day most pool names got changed to racial slurs?
Anyway, currently (nearly) every user has a fixed cap of 150 tag edits per hour. The only way to increase it is to have your account upgraded to Privileged, and there is no way to reduce it at all. If your tags are mostly invalid or even straight-up malicious, the only enforcement mechanism is the chance that someone will notice the common factor between a number of seemingly unrelated bad tags and report your account to the admins, a process that typically needs to happen a minimum of four times before the ability to change tags (as well as do anything else on the site) is taken away.
So I was thinking: what if the tag edit limit was dynamic, like the upload limit? The more valid tags you add, the more you can add per hour, and if someone deletes a tag you added, that goes towards your penalty count. Vandalism potential would be significantly reduced overnight, and even better, the much bigger problem of users not bothering to learn how tags work and doing untold amounts of damage without getting caught would fix itself given enough time.
This would also help significantly in the process of identifying good users, since the total number of posts edited says nothing about whether those edits were any good, and it's also possible to inflate it by adding tags to a post one at a time.
There is one major implementation hurdle that I can see: what to do about aliases? For what I assume are performance reasons, a new alias doesn't generate a post edit on its own, and instead credits the change to whoever edits the post next. Should this count towards that person's "good edits"? Should the person who added the aliased tag be penalised? Should penalties be conditional, like for replacements, since some aliases are more obvious than others? If they should be penalised, how to apply all the penalties at once and then prevent any of the penalties being double-counted in the future as posts are edited? If they shouldn't, how to prevent penalties being applied anyway for the same reason?
Bonus thought: invalid tags should count for extra karma, in both directions. Users are rewarded for patrolling invalid tags and replacing them with good ones (simply deleting a tag brings no rewards), and penalties are extra harsh if you add an invalid tag. Unlike uploads, rewards and penalties should be symmetrical, to encourage fixing your own mistakes.