I recently came across a production reason to use Edge Side Includes in Varnish, and I'm pretty happy with the outcome.
To help introduce folks to ESI and the possibilities it provides, I have created a simple demo repo showcasing some practical uses:
Check it out and tell me what you think!
I'm going to discuss this in person for the Feb 2016 meetup of the SA Web Dev group: http://www.meetup.com/sawebdev/events/228290389/
See you there!