@bamboo

subprojects {
    buildscript.repositories {
        mavenCentral()
    }
}

The above (in the top parent project) seems to make gradle happy; such that it resolves dependencies for subprojects. But without

buildscript {
    repositories {
        mavenCentral()
    }
}

(in each subproject) Intellij won't autocomplete for plugin extension types on the classpath. This may be a known bug that has been mentioned before; sorry about that if that's the case.