* Flynn builds apps from source, so not sure how that works for compiled Java/Go, or anything you'd run with a binary buildpack

You can deploy docker images, at least that was the case one year ago

* Cloud Foundry is run at massive scale in production for mission-critical workloads by banks, payment processors, IoT data ingesters, manufacturing companies, research companies, governments and everything inbetween. I can't see any evidence of the same being said for Flynn.

I think that's the whole idea behind flynn. Instead of being heavy-weight, complicated to deploy (no BOSH) and resource intensive, you can run a cluster with 3 nodes and deploy a ton of services there. It's not targeted at banks, it's targeted at people who don't want to use heroku or pivotal or GCE. And this makes it a lot faster in many ways, at least last time I checked.