I think it depends on which numerical bits though. Some people want to write Python that is fast, vs deferring the fastness to libraries in other languages (and/or using tools like numba or cython which transform Python into something faster). The former group seem to want no-GIL, and there's been a noticeable amount of breakage recently over CoW not being as effective as it use to be (which is reflected in the switch away from using fork be default on POSIX systems).