This issue look interesting for me, i am looking how to implement it.
If i have understand what you want to do.
For example.

• default severity could be
  high -> 5 , medium ->3 , low ->1, info ->0
• threshold for each alert define by the user
  high -> 0 , medium ->15, low ->10, info ->0
• culmulative threshold -> 20

When we run a scan, depending on the number of alerts in the report
we find the culmulative cost and for each level of alert.
we compare to the threshold and flagged the build as passed, failed or unstable.

I've attached an image with a more detailed explanation. Thank you for the support. If you have any questions please feel free to get in touch with me, also if you have any suggestions

thanks for your return.
I'm on another project actually, who occupies me now.
I will take a look at this feature, as soon as possible

Any idea on how to find the number of each alert severity.
without parsing the report.
i have seen there is a class alertsfile, and a method getAlertsFromFile, may be if i count alrte form that?
i am almost at the end of the issue. it 's the only think i have not done yet

Referencing Pull Request: https://github.com/jenkinsci/zap-plugin/pull/4

when this will be available? Any progress? Furthermore, if no one is working on it. I would love to work on this.