I want to use seed, but given that it is broken in Ubuntu Oneiric, I decided to support gjs. I chose to check for the existence of the Seed object, and construct one from gjs when it is not present. The namespace is still polluted. The interpreters have different command lines, though they are similar enough for my purposes.
I think the GNOME community could do better by updating the gjs and seed to share the same command line, and add extensions to a common namespace, such as System. Thus an app that wants to call System.print() will not care about which interpreter is used. This permits developer and distros to choose the backend of their choice. It also lets us change our minds.