"...it’s very easy to envision a future where CPython is used for command line utilities (which are generally single threaded and often so short running that the PyPy JIT never gets a chance to warm up) and embedded systems, while PyPy takes over the execution of long running scripts and applications, letting them run substantially faster and span multiple cores without requiring any modifications to the Python code"
IMHO this is the most sensible and logical approach and doesn't break any existing code. This also seems like what will likely happen anyways. Out of all the options PyPy-STM seems like the best approach because:
"pypy-stm is fully compatible with a GIL-based PyPy; you can use it as a drop-in replacement and multithreaded programs will run on multiple cores."
IMHO this is the most sensible and logical approach and doesn't break any existing code. This also seems like what will likely happen anyways. Out of all the options PyPy-STM seems like the best approach because:
"pypy-stm is fully compatible with a GIL-based PyPy; you can use it as a drop-in replacement and multithreaded programs will run on multiple cores."
http://pypy.readthedocs.org/en/latest/stm.html