At one point in his demo, he uploads a file but terminates the upload more or less halfway. Then he begins downloading the file - which only progresses to the point it had been uploaded, and subsequently stalls indefinitely. And, finally, he finishes uploading the file (which gracefully resumes) and the file download (which is still running) seamlessly completes.
I found that particularly impressive.
IIRC webtorrent /can/ do streaming though....