We should have an explicit task for ivy.xml generation. Also we should provide some hooks to manipulate the generated ivy.xml (possibly a separate ticket). I found this use case at the client's.

Current workaround.

Create an instance of Upload task but don't configure any repositories:

task generateIvyXml(type: Upload) {
  descriptorDestination = file('ivy.xml')
  uploadDescriptor = true
  configuration = configurations.myJars
}