Since I, personally, hardly know how to write readable code, I regret that I won’t become a contributor to this project.
Anyway, I would love to learn how to wrap os.scandir, until someone (who knows how to write readable code) has incorporated it into trio.
The way trio.Path.iterdir works would IMHO fit perfectly (given that I understand it right.) It seems to be an async constructor that calls os.listdir in a worker thread and then returns a regular generator (that does the actual yielding of results).
The main point is the DirEntry objects. 
I guess the main problem is the caching of DirEntry.stat(). If the data is in cache, you don’t really wish to await the result. But if not, you wouldn’t wish to block the execution.