Getting rid of the GIL is a big change. In py2.7 CPU-heavy threads are useless -- they lock up the process and starve other threads. py2.7 threads are only good

Getting rid of the GIL is a big change. In py2.7 CPU-heavy threads are useless -- they lock up the process and starve other threads. py2.7 threads are only good for I/O heavy work. You can use multiprocessing in py2.7 but with a lot of caveats if you want to share state and file descriptors. IMO the GIL removal is the one thing "that's not easily available via back ports in 2.7".