There was some limited discussion about pub-sub and a React based web-socket receiver. If someone took a lot of the complexity out of this it would solve your requirement of a web server initiated refresh on a callback that watched for new data on the socket. Here is a link to one of those discussions 
https://community.plotly.com/t/support-for-websockets/19348
I know this doesn’t answer your question but that would make dashboarding in DASH next level.
FRWZHR