In addition to reducing duplication between IPython and RStudio - it also shields them from low-level details and creates an interface we could more reasonably generalize to something like qsubing the docker commands or using Docker Swarm.
Rely on more Python and less on mako, setup a small shared common mako file in config/plugins/interactive_environments/common/ie.mako. Move ie.js into client/galaxy/scripts/galaxy.interactive_environments.js and extract IPython's require config out so it doesn't have to directly reference client/galaxy/scripts/galaxy.interactive_environments.js (I doubt it is where that file actually should be).
Pragmatically this allows visualizations to be enabled by default but not IPython stuff and provides a spot to put a warning about security issues. More abstractly I think it provides a nice separation (initially though superficial) between these plugin types.
Eric Rasche