About threading.excepthook() API, maybe we should not reproduce sys.excepthook() API but instead reuse something closer to sys.unraisablehook() API: use a single parameter which has attributes. It would allow to pass more parameters as new attributes in the future, maybe some new "optional" parameters (None by default).

For example, we can imagine calling threading.excepthook() to handle threading.excepthook() failure. We would need an argument to prevent an infine loop :-)