> About performances: it's fine to add anything to maybe_call_line_trace(), it cannot impact performances when tracing is not used.

I do not agree, Python debuggers are already really really slow. They should not have to process 'instruction' trace events as this would happen if George does "Remove the `else` to always trace with PyTrace_INSTRUCTION, rather than as an alternate to PyTrace_LINE as it does now".
I understand that this was a suggestion :)