I tried to build the python version of PlanOut with portability in mind. It took only a few minutes to port the base class that does all the hashing from PHP to Python. The the interpreter + a few core operators took about two hours. Developing the Experiment and Namespace classes to work in a way that we were happy with took a lot more time. I suspect that if you knew node / js, and just wanted to do a direct port, it shouldn't be too hard.

We have a little more background on the project at: http://facebook.github.io/planout/docs/about-planout.html and I'd be happy to review any ports to other frameworks.