If we are ever going to get rid of GIL, we need to get rid of Python's C extensions all together.
It is not a real Python implementation if not compatible with C extension, it is just embedded DSL that has Python flavor syntax.
It is not a real Python implementation if not compatible with C extension, it is just embedded DSL that has Python flavor syntax.
Is there really no situation in which an alternative implementation that only supports "pure Python" would be useful?
This really depends on your definition of 'being useful'. Jython is useful in a sense, it is being used in many Big Data solutions as a way to embed Python as DSL/UDF, like Pig/Hive, etc.
However, if without support for C extensions, it is not really a Python implementation, in a sense, I can't run a python script I just gripped from internet using the so-called 'alternative' implementation. So if the point of being useful is to be a replacement, then sadly, the answer is no, it is an everything-or-nothing situation.