I'm not all that familiar with Celery, but from what I can see, you'd essentially add a celery data component in your boxfile.yml. Nanobox would then build, provision, and network the component and allow you to connect to it with auto-generated environment variables.
Meteor is a really cool framework, but unique enough that it will require it's own engine (a set of scripts that builds and prepares your app's runtime)
Feel free to upvote meteor on the roadmap.