Sorry, I mischaracterised the way mod_wsgi works slightly. However, my understanding is still that the scope of this particular fix is merely to allow all external threads to be redirected to a different subinterpreter at various times over the life of a process. It does not need to allow different external threads to be redirected to different subinterpreters.

(Note: I am assuming that any hooks Apache/mod_wsgi has into external thread creation could already just create an appropriate thread state if that was the desired behaviour. It may be I'm incorrect on this, and what Graham really wants is the ability to change the target interpreter state just for the current thread. However, if that's what he wants, then there's additional background info I need on mod_wsgi and its ability to influence thread creation within a process, because I didn't get the impression on the weekend that that is what he was after)