-1. Libraries that manage their own tasks should continue to do so, until they are ready to adopt TaskGroup. Trying to "own" (and wait for) tasks created by a library sounds like a recipe for disaster if the library wasn't expecting that.

Do you have a specific use case or scenario that has bitten you in the past? If you want to continue to argue for this feature we would need specifics (not a link to reams of code but a clear story telling of a problem you've encountered in real life in the past that your proposal might solve).