That's exactly what ReleaseHub is :)
Do you have an example of what you're describing that can't be easily solved by docker-compose?
We are a full CI/CD platform with the ability to do static javascript builds, build-x builds, installing in our customers clusters, installing in their customers clusters, dealing with routing for ephemeral environments, creating pools of resources for ephemeral environments to attach to, deploying and monitoring production environments, a workflow engine and we are just getting started!
We do run into objections along the way like, "can't a couple of people do this pretty easily", but depending on what you want to do, it grows in complexity quickly. A lot of time teams don't realize that until they are way down the path of trying to create a system like this.
If you have any specific questions about how ReleaseHub works let me know, happy to answer anything!
Docker-compose only runs on my (your) laptop. What if you want to share that with someone else? I have to git stash, checkout a branch, tell someone else to do all that... I think you're on the right idea: it's "easy" to do with existing tooling, but there's a big gap between it's easy to do and then go and spend the time to do it.
It is important to understand trivial doesn't always mean fast and easy. Also "easy" is a matter of perspective.
If you're using a PaaS that offers this, you (99.9% of the time) shouldn't look elsewhere. Just use their offering.
If you're not using an explicit PaaS, rebuilding this functionality yourself can end up being a never-ending rabbit hole.
Heroku review apps are analogous to our ephemeral environments, but we can deal with much more complicated environments, which reduces complexity in your CI/CD platform, production deployments or on-premise deployments if needed.