The ban process is very useful to preventing low quality posts - for the most part. One very large glaring issue with it is that users can bypass it at will by using a different account.
On a daily basis users hit the ban, and then either bypass it or take to meta to figure out why it happened and how to fix it. Their questions are a constant flow and have been for a long time, this should come as no surprise.
Being banned from anything is rather jarring. In this instance, I know that it is meant to be. However, I feel that if users feel more invested in their account then they will not bypass the ban. Bypassing the ban is a problem I think we can work on.
Users would feel more invested in their account if they were allowed to build more content before being entirely shut out. Being shut out so suddenly is the "cold turkey" reference I make.
"Cold turkey" describes the actions of a person who abruptly gives up a habit or addiction rather than gradually easing the process through gradual reduction or by using replacement medication -wiki
I think that question bans would be more effective as a throttle than as a cutoff.
For users who hit the ban, as opposed to a complete stop, begin throttling their posts.
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Have the limit be constrictive, and approach 0 but never hit it. Perhaps when the user first hits the ban limit them to 1 post per week. As the metric used for the ban progresses negatively, increase the week count. Using this approach, after another 4 posts if each one made the metric worse, then perhaps it would have taken then 1 week for the first, 2 for the second, 3 for the third, 4 for the fourth (assuming a +1 for each decrease in the metric score) -- meaning it took them 10 weeks to make another 4 low quality posts.
The benefit is that if they had rerolled their account, this would have taken them a mere 1 day to make another 4 low quality posts. Moreover, they feel they can still provide content at some point and also feel more invested in their account as it progresses.
This would also allow them a possible path to redemption at some point if they were able to begin to work well enough with the system to climb out of the throttle.
tldr;
Significantly throttle posts of banned users instead of preventing them from posting entirely.