> perhaps there will be a flag to selectively operate a python process without the GIL (and leave the onous on you to completely test and validate your code works with potentially new and spooky behaviour).

Worked for ruby. The original interpreter MRI has a GIL too. Rubinius and JRuby added multi-threading with limited amounts of pain and people fixed libraries over the years. Sometimes just sprinkling lock blocks around a particular FFI calls or only doing them from a dedicated thread will do the job.