Given how limited RPython is, are you sure RPython is not Python 2/3 compatible as is? What Python 2 only features it uses? The faq that you've linked says tha

Given how limited RPython is, are you sure RPython is not Python 2/3 compatible as is? What Python 2 only features it uses? The faq that you've linked says that RPython will continue to run on Python 2 as long as Pypy exists, it says nothing about running RPython on Python 3 interpreter.