So, in 4.13 there will be the AsyncTask function, which does exactly what you want. That being said, I’m not too happy with the name (should probably be ExecuteOnThread), and there are some concerns about wrapping the task graph system in this way. You can start using it, but it needs a little more thought, and it may change in the near future.
What we really want is an API for continuations similar to what is possible in .NET and some JavaScript frameworks (DoThis(…).ThenThat(…).AndThis(…).OrThat(…) - you get the idea). It is not yet clear how this would be implemented. The CompletionCallback on Async and the new AsyncThread is also a bit of a hack and not all that useful. I need to find some time to think about this some more and provide a cleaner and more useful API for chaining multiple tasks. Consider the current features as a stepping stone in that direction.