> Is there any progress on the issue? Should someone take over?

It's a limitation of the libc, not directly of Python.

The problem is that the sem_timedwait() function of the glibc doesn't allow to specify which clock is used:
https://sourceware.org/bugzilla/show_bug.cgi?id=14717

Someone has to contribute to the glibc to add an option to sem_init() or sem_timedwait() to allow to use a different clock than CLOCK_REALTIME.

One workaround is to use Python to use the mutex+cond implementation of pthread locks, since this one is already able to use CLOCK_MONOTONIC:
https://bugs.python.org/issue31267#msg302257