Rather than allowing this on tracebacks directly, I'd prefer to build on the "TracebackException" work and allow traceback summaries in all the places where we currently require real tracebacks (including exception __traceback__ attributes): https://docs.python.org/3/library/traceback.html#tracebackexception-objects

The essential requirement here would be to abstract out a "traceback protocol" from the current concrete traceback objects, and adapt affected parts of the interpreter (such as the traceback display on shutdown) to use that abstract protocol when dealing with a non-native traceback object.