...OK, I have [some code that appears to work](https://gist.github.com/snej/653856212361be805751e4208a87d131), at least in Nim 1.2.2 with gc:orc. It lets you
* Wrap a Future in another Future that can be passed to and completed on another thread, and will then invoke the original Future on its original thread (so it works correctly with `await`.) * `spawn` a proc and get its result as a `Future` instead of a `FlowVar`. Feedback is more than welcome.
