You are right. It's very similar to vagrant. When we started implementing our idea, we did not know about vagrant.
The vagrant functionality is part of what we do, but we also have a hosted service and offer access control to your team. We also have a mechanism to synchronize changes between your envs
How will this work? It sounded like a user could just build a custom VM image and send it to you. There wouldn't be a way to deploy that to heroku, right?
Are you doing sort of a blended app hosting/cloud offering?
Have you seen the dotcloud "build files" for specifying services? I wonder if trying to encourage standardization among cloud/app hosts on a service specification file like this would be beneficial, similar to Gemfile/Procfile/etc.
The vagrant functionality is part of what we do, but we also have a hosted service and offer access control to your team. We also have a mechanism to synchronize changes between your envs