At this point, one-click (or one command or one PR open) pre-production environments are almost table stakes for PaaS offerings. This kind of functionality was the primary reason we moved from self-hosted to PaaS (Pantheon) back in 2012/13 at a prior gig. Heroku (as mentioned in other comments) offers similar functionality these days.
Given you probably won't have much traction with teams who are happy on PaaS offerings like the aforementioned, am I right in thinking your market is either people doing completely bespoke docker stuff (how many of those are there), or people whose apps don't neatly fit (either due to size or complexity) into an existing PaaS offering?
If that's the case, I wonder if docker is the wrong abstraction-point. Perhaps it'd be better to be a glue layer between a VCS and something like a Terraform configuration or a Pulumi project.
I also wonder an open source model could be a winner here, too.