git - project evolution, branch or new repo?

Я разработал веб-приложение Google App Engine, версия которого размещена на GitHub.
I'm going to "port" this application making it GAE agnostic; this port would have several files in commons with the original project but also a different file system structure.

Is it better to create a new branch (nogae) and work on it or is it preferable to create a new git repo (project.nogae)?

What's the pros and cons?