Just a few points that I would request you to dig further.
1. Quick immutable envs aren't so much of a problem for B2C apps. Particularly for B2B apps, it's not just the "run-build--pull-image--deploy--start-svc--share-url" that's the real hard part. The real hard part for B2B apps is the test data - the sane dataset which needs to be replicated as well, per environment. Nobody wants to use a test/staging DB where changes are uncontrolled. Bottomline - Immutability isn't just at the app layer, has to cover the test data and stateful parts (datastores) too.
2. What's the real value of it? One possible way to figure out hassle-to-value ratio, is the ratio of number-of-commits to number-of-builds, and the ratio of number-of-builds to any number-signifying-quality. If more builds (=> more number of envs cropping up, and brought down, that is a high rate of env churn) do not mean increased quality, then anyone choosing such a solution is really just doing it for the sake of feeling self-important or sounding smart.
One really has to be keenly tuned for the real business value, while validating fitment of such tools for the org/business.
Happy to discuss more. I have been designing/building tools like this, as a day job for quite some time.