It sounds like we want to temporarily revoke a person's ability to make lots of posts when recent quality is an issue.
The Participate Everywhere ability allows one to post without limit. Nominally, the requirement to earn it is:
To earn this ability, you need to have roughly 75% of your posts be positively received, with a minimum of 5 positively-recieved posts (these numbers may vary from site to site).
I said "nominally", because we've started communities here in "new" mode, so that people trying to build and expand our small communities aren't, um, hobbled.
Without "new" mode, people start at Participate:
This ability allows you to posts 3 top-level posts (questions and articles) a day, and to post 20 answers a day.
This ability also allows you to raise 15 flags on posts a day.
Three posts a day is hobbling, not a block, so people can lift themselves out of it.
Moderators can suspend or revoke individual abilities. I know this question is about automatic measures, but there is a manual option for individual cases that are disrupting a community.
The system automatically checks qualifications periodically (I think a few times a day) and grants new abilities when people have earned them. It does not currently revoke abilities (and in some cases that would be hard to even test).
Question 1: Should we build a "hobbling" system on the same tools? If the criteria (TBD) are met to tell a user to slow down, the script could suspend Participate Everywhere. Later runs of the script would check whether conditions have improved and restore the ability if so.
Question 2: If so, what should the criteria be to hobble a user? Abilities are based on all activity, but it seems like the problem that motivated this question arises from recent activity. If somebody had a bad start a year ago, fixed it, and then has one bad post now, that shouldn't hobble the person, I don't think. But if several more bad posts follow, that's different.
No matter what approach we take, I think it's important to give a user some warning at posting time -- something to the effect of "hey, be careful -- several of your recent posts haven't been well-received and you might get rate-limited".
If we take the approach I'm describing, then the only timing problem would be if the script happens to run while the person is posting. We can probably catch and handle that so the person doesn't lose work. (It'd stink to write up a long answer and only then have it rejected.) Otherwise, we know when you click "ask question" or start to type into the answer box whether you're allowed to post right now, and we can intercept you if not (like we do with existing rate limits).
By using the abilities system, we reduce the chances of creating weird conflicts with the abilities system by having two different, parallel ways of deciding what you're allowed to do. That seems more resilient.
A final question: Should we lift "new" mode from any network communities and recalculate abilities? I'll have to check with devs to find out what other effects there are; I think it's mainly that in "new" mode everyone starts with Participate Everywhere, but if there are other effects too, that would factor into the discussion.