Oh, I forgot to mention why this  matters:

If it's `TaskKey[Seq[Taskkey]]` and you do an `inspect tree` of the key, you *don't* see all the tasks that will be run.  If it's `TaskKey[Seq[Task[_]]` then you *do* see all the pipeline tasks, since the you're past the "Initialize" layer, and all the dependencies are known.  So really, you should prefer using `Task[_]` here for that reason alone.