> This is more to my point: I found the TypeError message not clear at all. 

> From my prospective, I was using a future object returned from an asyncio function to call another asyncio function, yet that function was telling me it could only use a future with it. 

I understand, but this is the first time I see somebody tries to use `ensure_future` on `run_coroutine_threadsafe` result, which suggests that it's not a common problem.

Specializing error messages makes code more complex and adds to maintenance overhead, so we can't afford to make changes on first request.  In cases like this we usually put the issue on hold to see if more people complain.