I seriously doubt it, considering a) RPython is a strict subset of Python, operating on the in memory representation of Python objects and does aggressive type

I seriously doubt it, considering a) RPython is a strict subset of Python, operating on the in memory representation of Python objects and does aggressive type inference, whereas Cython adds additional features (and syntax) to the language and has it's own parser and no type inference (AFAIK), and b) RPython predates Cython, AFAIK.