Thanks for this great plugin! Right now we can use throttleConcurrentBuilds to configure basic throttling on a matrix job, but by default, this only configures throttling for the parent job. To configure throttling for the child builds and not the parent, we use this workaround:

throttleConcurrentBuilds {
    categories(['our-category'])
}
configure { project ->
    project / 'properties' / 'hudson.plugins.throttleconcurrents.ThrottleJobProperty' << 'matrixOptions' {
        throttleMatrixBuilds(false)
        throttleMatrixConfigurations(true)
     }
}

It would be great to configure those options directly with job-dsl for matrix jobs.